Building the Symbol of a Remarkable Transformation

March 27, 2017

Iker Gil interviews John Zils, SOM Associate Partner Emeritus, a key member of the structural team for the Guggenheim Museum in Bilbao as well as other notable projects, including the Sears Tower in Chicago.


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Guggenheim Museum. © Courtesy of Gehry Partners, LLP.

If there is a building that symbolizes the transformation of Bilbao and put the city on the international stage, it is the Guggenheim Museum in Bilbao. It was in October of 1997 when the building opened its doors to the public becoming, almost instantly, one of the most remarkable and recognizable structures of the twentieth century. Almost two decades later, the Guggenheim continues to attract one million visitors a year, all as interested in seeing the blockbuster exhibitions on display as much as visiting the building itself.

Designed by Frank O. Gehry & Associates, the building was a feat of design and construction. The use of digital modeling, including the now famous CATIA, and other innovations opened the door to a new generation of architecture that defined in the beginnings of the twenty-first century. The Chicago office of Skidmore, Owings & Merrill (SOM), one of the leading architecture and engineering firms in the world and responsible for many remarkable buildings in their own right, served as the structural engineer for the building with Bilbao-based IDOM as the local engineer. It was a unique collaboration that proved to be a major success.

Earlier this year, we had the pleasure to talk with John Zils, SOM Associate Partner Emeritus, a key member of the structural team for the Guggenheim Museum in Bilbao as well as other notable projects, including the Sears Tower in Chicago. John shared with us the history of the structural group at SOM, the origins of the collaboration with Frank Gehry, and the process of a building project that would become a turning point for a city as well as the career of its architect.

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Guggenheim Museum model. © Courtesy of Gehry Partners, LLP.

IG: You joined SOM in 1966, so you have been directly involved in shaping many of the great projects of the office. Can you talk about the early period of your career at SOM?

JZ: That period starts with Fazlur Khan. To a great extent, it also starts with a gentleman by the name of Srinivasa “Hal” Iyengar, who joined SOM a couple of years after Faz. The two of them were instrumental in developing the structural group as we know it today, fostering an integrated process of work between architects and structural engineers. It had always been part of SOM’s philosophy, but I think it was really brought home by them.

The second thing that was important in that period was the advent of the computer. Very early on after Faz and Hal joined SOM, they realized that the computer was going to be a very important tool in our profession. Not only our profession, but the whole building profession. They convinced the partners at SOM to get a computer for the office. It was really for the structural group, as the others groups weren’t going to get involved initially. The advent of the computer then led to all the investigations and system developments that Faz was involved in with high-rise buildings. It started with the Dewitt Chestnut Apartments built in 1965, which was the first tubular building, and then progressed to the John Hancock Center, Sears Tower, and many others. All of them would not have been possible without the use of the computer.

IG: What year did SOM buy the computer?

JZ: Faz joined the Chicago office in 1960 and I think the first computer was brought into the firm around 1961.

IG: That was very early. Did you know of any other architecture office that was using the computer at the time?

JZ: I don’t, but there probably were a handful of them. To say SOM was the only office wouldn’t be fair, but it was very, very early. The computer played a very important role in the development of these different structural systems that were all offshoots of what we term the tubular concept of behavior in a high-rise building. When I joined SOM in 1966, the design for the John Hancock Center was really just being completed, so I really didn’t get involved in that building. I was involved with another building, the 31-story National Life Building [now the William R. Snodgrass Tennessee Tower] in Nashville, Tennessee, with Hal Iyengar and Faz Khan. That was my first exposure, so to speak, to high-rise design and high-rise buildings. Then I left the firm for two years to go in the Army, coming back in January of 1969. Very shortly after that, I got involved in the Sears Tower with both Faz and Hal. I was the project engineer for the Sears Tower, following it all the way through completion of construction. That project brought on many new developments in terms of structural systems, the bundled tube, and other components of the structure, which were very unique to Sears Tower. There was always this attitude toward economy and integration of architecture and structure.

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Sears Tower. © Ezra Stoller | ESTO.

IG: Did the architects and engineers work together from the beginning in those projects? Clearly the structure is one of the aspects driving the aesthetics of the buildings.

JZ: When you’re dealing with a 100-story building, you have no choice. You have to integrate the structure and the architecture.

That same philosophy, if you want to call it that, pervaded all the projects, whether it would be a two-story building, a long span building, or a mid-rise building. Faz and Bruce Graham [architectural design partner] in particular developed a chemistry between them where Bruce and Faz wouldn’t proceed without each other. There was a very strong connection between the two of them and that connection pervaded down to everyone in the firm. There was this idea of a group practice where the various disciplines work together right from the beginning, particularly the structure and architecture, but also the MEP group and all the other disciplines. I’m a firm believer that that’s the only way to design buildings. Again, whether it’s a hundred stories or it’s two stories, there’s an appropriate structure for each building. To this day, I think the firm still works that way. It’s because of these people. A lot of the things that developed, a lot of the architecture that we designed and built, would not have been possible without that collaboration. It never would have happened, whether that’s the Hancock Center, Sears Tower, the Hajj Terminal in Jedda, Saudi Arabia, Onterie Center here in Chicago, Hotel Arts in Barcelona, or the Guggenheim Museum in Bilbao.

We tried to instill that same philosophy with Frank Gehry. It worked differently than it would work here at SOM, where you are right in the same building and shoulder to shoulder with people, but I think it worked pretty well. A lot of times people will ask me, “How in the world, with the kind of architecture you do at SOM and the way SOM works, could you work with Frank Gehry?” I have to tell you, it wasn’t the same as working at SOM, but I think we were still able to engender that spirit, that philosophy, which Frank was quite receptive to. A lot of people think his designs are just whimsy. They’re not. He was very receptive to our structural input and what we were doing. We were involved right at the very beginning in his projects.

IG: The first collaboration with Gehry was related to the Hotel Arts in Barcelona designed by SOM and built for the 1992 Olympic Games. Next to the hotel, there is his fish sculpture.

JZ: He was involved with the fish and he was also the design architect of the retail portion.

IG: I actually never knew that the retail area was his, too.

JZ: Yes, he was the design architect for that portion in front of the Hotel Arts tower, but the real collaboration was the fish in terms of our introduction to working with Frank.

IG: How did that collaboration take place?

JZ: Bruce Graham brought Frank to the project. I can’t really tell you what the impetus was for that, other than they knew each other and had a relationship of some sort in terms of knowing each other professionally. Again, he was brought in as the design architect for the retail portion and the fish. We worked with Frank and Jim Glymph, who was at that time the person leading the CATIA effort. They developed this whole kind of offshoot of the architectural office, a technology group which brought on CATIA and developed a lot of things. We worked really well with Jim and Frank on the fish sculpture. As that project finished in 1992, our involvement with the project in Bilbao started.

IG: The competition for the Guggenheim Museum took place in 1991. Frank Gehry was an advisor for the project and later was brought in as one of the three participants for the competition, the other two being Arata Isozaki and Coop. Himmelblau. It was in July of 1991 when Gehry won the competition, so it was right around that time.

JZ: We were brought into the project in early 1992. Based on our experience with him that had just concluded in Barcelona, he then asked us if we would like to join him in this project in Bilbao. We knew it was going to be a major project, but I don’t think that at that time we had any sense that it was going to be quite as significant as it turned out to be. But we knew it was going to be a major project and we were happy to be a part of it.

Frank sent us a letter that included a sketch and he said, “Now that you’ve done a fish, would you like to do a flower?” He asked if we would submit a proposal for our structural engineering services. He sent us that sketch and he told us how many square meters the project was going to be. He expected us to give him a fee, and we did.

IG: Out of that sketch?

JZ: Yes, the sketch and the square meters. We were silly enough or whatever you want to say to do it.

IG: I guess it really helped that you had worked with him before and you had built a solid relationship.

JZ: Yes. So that was our introduction to the project in Bilbao.

IG: How far along was the design of the project when you got involved? Was Gehry still primarily working with sketches?

JZ: Yes. When we actively got working on the project, he had done a few sketches and I think he probably had an initial model. I mean, he built so many models, that’s how he works basically, so there was probably a model or two. I don’t remember exactly but we got involved very early on.

IG: How were the architectural ambitions set between the two offices?

JZ: There was a lot of back and forth. There is an interesting story about the very first team meeting we had. We went out to Santa Monica, where his office was at that time, and he probably had a model and maybe some sketches. We were talking about the project, and at one point Frank turned to us and he said, “You don’t have to worry about the structure because we think it should be reinforced concrete. With all the curves and shapes, reinforced concrete is what the structure should to be.” We said, “Well okay, we’ll take a look at it.” That’s how we started, you might say not in the right direction.

As we got home and started looking at things, we quickly realized that concrete was not the right solution. This project was going to be of a scale and complexity that Frank had never worked at before. Most of his previous projects were smaller in scale but this one was a whole different ball game. As you know, in the atrium of the Guggenheim, the flower as he called it, there were surfaces that were 150 feet in the air with nothing under them. We realized very quickly that concrete was not going to work very well because in the flower atrium you were going to have to scaffold all the way up there to support all this form work and concrete way up in the air. It was going to be very expensive. So we started looking at alternate solutions. We had a series of meetings, going back and forth to Santa Monica with Frank, looking at wood structures, looking at steel structures, looking at precast and a lot of different options. The more we looked at it, the more we realized that steel was going to be the right answer. First of all, Bilbao is a steel city, with all the shipbuilding and a phenomenal technical expertise. It’s terrific. Concrete is really economically feasible only on a small or less complex scale.

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Guggenheim Museum under construction. © SOM.

IG: There’s a rich history in Bilbao of working with steel related to shipbuilding and other industries, mostly at a larger scale than is typically associated with the scale of a building.

JZ: Let me also back up a minute because, very early on, there was a process to bring on the contractor which was very important in this project. Very early in this project, we had a whole series of meetings in Bilbao with various contractors and eventually IDOM was selected. It was a terrific selection. Not only were they very good technically, but also they were very adaptive at working with us. We had a very good communication with them and understanding of the process for the project. I really have to give them credit for that.

Having IDOM on the team also helped in looking at the various structural systems and what would be possible and what wouldn’t. After a series of meetings with Frank, he eventually understood that concrete probably wasn’t the best choice and he agreed that we should pursue the steel option. That seemed like the right way to go, but that wasn’t the end of the story because we still hadn’t worked out what we thought the system was. We just knew steel was the right way to do it. We probably spent two months studying what was the appropriate system for structural steel. We knew it had to be able to conform to the different shapes, it had to be economical, and it had to buildable, because no two shapes were the same. Everything was different, very complicated.

One of the key things that separated the steel from concrete was that there was no need for shoring or stabilizing cables, no construction hindrances so to speak. We wanted to be able to erect the structure without temporary props, something that would allow us to greatly reduce the cost. In fact, the final cost of the steel structure for the Guggenheim Museum was exactly the same as if we were building a rectilinear building with 30 feet by 30 feet bays, steel beams, and girders. The steel per ton cost was exactly the same, which was a real accomplishment, because it is a complicated structure.

There were ways to achieve that. One of the things that we came up with was what we called a lattice steel grid system. It was a structure that would replicate a wall in terms of its behavior. We did this by creating a series of vertical and horizontal planes on a module that then would form this wall-like structure, but it was made out of steel.

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Guggenheim Museum under construction. © SOM.

IG: What was the size of the module used?

JZ: If I remember correctly it was 10 feet by 10 feet, about 3 meters by 3 meters. One of the advantages of this is that it could span long distances. This had a lot of strength to span a large distance with just being supported at each end. We worked for two months sitting in a conference room with sketches and yellow paper trying to figure out what was the right approach. We were not doing a lot of calculations, just trying to come up with the right system. Now you look back on it and you say, “Well gee, that’s very simple and very obvious.” Well, I’ll tell you it wasn’t obvious at the time.

IG: Did you look at any precedents when thinking about the structure?

JZ: No. It looks so simple and so straightforward now but it wasn’t then and it had never been done before. In fact, the structure system ended up winning the American Society of Civil Engineers Innovation of the Year award. They give this award for innovation to one project in the world. Just one.

The next important decision was to see if we were going to build the structure flat, like a flat wall, and then create a secondary line of support to create the curve, or if we were going to curve the structure. Very quickly we realized that there was a huge advantage in curving the structure. I could certainly demonstrate that if I take piece of paper that is flat and I hold it out, it doesn’t have any strength at all. The only way to make it stronger is to add more material. If you curve it, now you’re taking advantage of the geometric stiffness, not the material stiffness.

IG: So you need less steel.

JZ: Correct. That’s the main thing, that you need less steel. All of a sudden it’s very stiff, but if you make it flat, then it is not. Then you need very little additional steel to support the wall itself because the structure is going to follow the curve. The other thing that it does for you is that it creates more interior space. If you have a flat structure and then have to curve the wall surfaces, you have a huge cavity there eventually.

IG: And that is space that is not usable.

JZ: It’s not usable. With our system, all of a sudden you have generated a lot more interior space for no extra cost. So the decision was to curve the structure. When Frank heard about it he was just elated, because instead of fighting the curve, we used it. So the curvature was very important not only to him; it was important to us too, and he didn’t have to pay any penalty for it. In fact, it was saving money.

During the design process later on, as we were doing the design and the analysis, there was one area where we were having difficulty making it work properly. It was too flat. We had a meeting in Santa Monica with Frank and we said, “Frank, we’ve got a problem. In this particular area, this wall is too flat. It doesn’t have enough stiffness. We really need more curvature.” He said, “This is amazing, I’ve never heard structural engineers come to me and tell me they want to make more curvature. They’re usually telling me just the opposite.”

IG: One of the things that I find interesting is that the building has a lot of volumes that are very different in shape. You have some that have a lot of curvature and others that that are much more flat. I am sure that the flexibility of the structural system to take on the curves had to be one of the key aspects.

JZ: We had listed some of the aspects that we had to take into consideration while designing the structure of the building: it had to be versatile, and take any curve, any shape; it had to be disciplined, organized, and economical; it had to be fabric-like; It had to be thin to minimize the wasted space; we obviously had to be able to analyze it and do our calculations; it had to be lightweight and we had to be able to control the shape very closely. It was very important to Frank that the curves that he wanted were the curves that ended up in being built. We had to be able to do all of these things to satisfy his requirements.

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Guggenheim Museum, Bilbao. © Iker Gil.

IG: Let’s go back to the flow of information between the office of Frank Gehry and SOM. Can you go through the process as you were both using very different design methods?

JZ: The physical model was probed and then digitized. That information then was sent as a DXFO CAD to SOM where we used our own software that we called AES to do our analysis and design. Then we would send these wireframes to Frank’s office and they would check them to make sure that something didn’t get changed in the digital models. We also needed to make sure that the structure wasn’t protruding over the curved finished surface. There wasn’t a lot of room for errors.

The other interesting part of this story is that, at this time, which was the middle of the 1990s, the fabricators in the US had no capability electronically do shop drawings. All shop drawings were still being done by hand in the US. When we worked on this project, we were amazed that the fabricator had selected a firm in Belgium who had the capability of producing electronic shop drawings. There had been some discussions in the US, but nobody seemed interested in it. This project would have just been a nightmare to do by hand. The company from Belgium created very good shop drawings.

IG: Was that company working exclusively on architecture projects or were they working on other type of projects?

JZ: I think it was for other things besides architecture. There might have been bridges and other civil structures, but I’m not sure. They were using a software called BOCAD. The interesting part of this story, too, is that they said that they had tried to bring BOCAD to the US. They had come to the US, met with some fabricators and detailers, and nobody was interested in it, so they gave up and went back. This was the process that we did go through at that time.

IG: It is fascinating to learn about the behind the scenes of how this happened.

JZ: Obviously it would’ve been simpler if we had the CATIA capability at that time, but it really didn’t cause any problems. Subsequently we did get CATIA, but this project was so early on that we hadn’t really gotten into that then.

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3D drawing for the Guggenheim Museum. © SOM.

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3D drawing for the Guggenheim Museum. © SOM.

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3D drawing for the Guggenheim Museum. © Courtesy of Gehry Partners, LLP.

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3D drawing for the Guggenheim Museum. © Courtesy of Gehry Partners, LLP.

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3D drawing for the Guggenheim Museum.

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3D drawing for the Guggenheim Museum.

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3D drawing for the Guggenheim Museum.

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3D drawing for the Guggenheim Museum.

IG: Now that you had the design and the shop drawings, let’s talk about its fabrication and building of the structure.

JZ: When you look at the structure, it really is just a series of bands of trusses forming a wall. These are really nothing more than trusses.

IG: So it’s like stacking one truss on top of another one?

JZ: That’s the way it was fabricated. It was brought out to the site like that. It had the ability to span across these distances, then you put one on top of the other one, and then connected them. Obviously it kept getting stronger and stronger as you put them on so, when you finally did get the whole shape in place and started connecting floors to it, it had that ability to span long distances. There was virtually no shoring, no guide wires, nothing. The whole structure was just erected one on top of the other. That reduced the cost greatly.

IG: Were all these elements fabricated in Bilbao or nearby?.

JZ: It was actually up in Vitoria by a joint venture between URSSA/Lauki/Ferrovial. An important part was what they did in the fabrication shop. As they would get each one of these elements fabricated, they would put them together in the shop to check that they all fit together and that the tolerances were met properly. So when they brought it out in the field and put it up, they didn’t discover that things were not right. Every shape was preassembled at the fabricator to make sure that they were correct and then disassembled and brought out to the site and erected. The problems at the site in terms of erection of the structure were minimal, absolutely minimal.

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Intermediate joint. © SOM.

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Intermediate joint. © SOM.

I attribute a lot of that to IDOM. In particular, they had a very good structural engineer called Amando Castroviejo. He was just on top of everything. We would communicate all the time, he kept us up to date on what was going on or whatever. I have to tell you we really completed the project without any major structural issues. There were some small things as we went through, but very minor. Part of that I think was the work we did, but part of it was the work they did over there, too. Just keeping an eye on everything and making sure it was going in the right direction. So I give a lot of credit to IDOM, they were very good.

The other anecdotal part of it that’s kind of interesting is that right as the structure was being completed, Frank Gehry came to the site and looked at the structure. He hadn’t been there in a while and he was amazed. His feedback to us was, “If I had known that the structure was going to be this elegant and this beautiful, I would have exposed some of it. It’s a shame that we’re going to cover it all up.” It really was a beautiful structure. Very light, very elegant, it looked like it belonged.

IG: When I see an image of it under construction, it reminds me again of shipbuilding, like in the Euskalduna shipyard that existed right next to it before. And it is a scale of infrastructure more than of a building. It is interesting that, in its final state, only in the tower can you see some of the structure exposed.

JZ: That beauty isn’t represented, unfortunately. The structural system in the tower is not the structural system of the building, so it would have been nice if somehow the building could have been exposed at some point.

IG: It’s quite amazing that it only took six years from the moment the building was commissioned in July of 1991 until it opened in October of 1997. It almost seems impossible nowadays.

JZ: Really, the work didn’t get started until 1992. The first year, there wasn’t much going on.

IG: It seems that constraints also worked in your favor. It had to be built in a relatively short period of time and you had a specific budget, so you had to simplify as much as possible the construction of a complex building.

JZ: That’s the other thing. Strange as it would seem, the budget that the city had was very, very, very tight. There was no going back and forth on this thing. So things were very carefully monitored by the city and by everyone involved to make sure it didn’t get out of hand. One interesting aspect of that is the exterior cladding. I don’t know if you know that story or not. It’s titanium, but the original project was stainless steel. The only reason the Guggenheim ended up using titanium was that, precisely when the drawings were issued for construction, Russia dumped their entire reserve of titanium on the world market. The price of titanium went out the bottom. Just pure luck. We quickly bought all the titanium for this project, and shortly after, of course, the rest of the world bought up all the titanium too, so the price went skyrocketing again.

IG: Until that point, titanium wasn’t a material that had been used before in architecture as a cladding material due to its cost.

JZ: Frank had identified it as a material that he would like to use in one of his projects. It had never happened prior to that and it didn’t look like it was going to happen in this project either. Then all of a sudden, boom. Sometimes you are just in the right place at the right time and that is what happened here. As you know from being out there, the effect of the titanium is really interesting because it can change completely depending on the light conditions, if there are clouds, or if it’s sunny.

IG: Mostly clouds. That’s what we have.

JZ: Mostly clouds, right. But it can take on a completely different appearance. Sometimes it can be gold, sometimes it can be pink, silver… all different colors.

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Titanium panels, Guggenheim Museum, Bilbao. © Iker Gil.

IG: And you have the backdrop of the mountains too. It’s a building that you think you know and, in reality, it presents itself in a slightly different way everyday you see it.

JZ: It’s a very dynamic building in terms of its appearance.

IG: When I was in high school, three of the students and two of our professors visited the building when the structure was exposed. It was impressive and exciting, but also intimidating and foreign. It was a very interesting moment, but I remember I didn’t have the sense of the impact that the building would have.

JZ: I have to say that by this point we were aware of its impact, but at the very beginning we weren’t. We knew it was a major project, but we didn’t exactly grasp the full extent of its impact. By the time we got to the structure going up, you knew it was going to have a major impact on the city.

IG: After the Guggenheim Museum, you worked with Frank Gehry in other projects in Chicago, like the Jay Pritzker Pavilion and the pedestrian bridge, both in Millennium Park.

JZ: That’s about it. We have talked to him about some other projects and it just hasn’t worked out.

IG: Did having worked in Bilbao simplify the work in the projects in Chicago, for example in terms of defining the structural system?

JZ: Yes, because in Chicago we did approach the surfaces the same way we did in Bilbao. The support of the surfaces is entirely different in both projects, but we approached the surfaces themselves very similarly.

IG: It’s interesting that in the Pritzker Pavilion in Chicago, you do see the exposed structure. From the front you don’t see it, but you do from the back or the sides.

JZ: To be honest, it’s not quite as pure as the one in Bilbao because of all that support that goes in the back. In Bilbao, the structure itself is the support.

IG: Have there been collaborations with other architects in a similar way to the collaboration with Gehry’s office?

JZ: On a smaller scale. Up until the work with Frank Gehry, our structural group at SOM had never worked outside of the firm. The project in Barcelona and bringing Frank Gehry on was the very first time our structural group had worked with an outside architect. We still continue that today, and the philosophy is that our structural group can work with outside architects, but they have to be architects that are in a non-competitive type of project. We would never design a 100-story building for an outside architect. At least I’ll say today, never say never.

IG: Did the way you approached the Guggenheim Museum influence subsequent projects at SOM?

JZ: I would basically say no. We approached this building much as we typically approach a structure in a building here at SOM. Now, as we said, there were some differences, because we were working with Frank Gehry in Santa Monica and we were here, so not quite the same as a regular SOM project, but very similar. I would say from that aspect it, did not really change anything. This is just a reflection of what we do.

One interesting thing that happened was that, when the project opened in 1997, the architecture critic from the Chicago Tribune, Blair Kamin, went to Bilbao to see it. The headline of the article he wrote when he came back read, “Guggenheim Bilbao gets a Chicago Structure.” What he meant by it was that, even though the project was a very complicated and very different kind of project from ours at SOM, we did approach it the same way and we came out with a very disciplined approach. We took complication and simplified it to build it. That’s what he explained in his article. We really hadn’t talked to him that much, and he was very perceptive in seeing that these guys from Chicago brought their very systematic approach and it worked.

IG: Have you been back to Bilbao after the Guggenheim Museum opened?

JZ: No, I haven’t been back since it opened unfortunately.

IG: The city has changed a lot in these almost twenty years.

JZ: I’m sure it has. When we first started working on the project and I would go over there, I really felt like I was one of the few non-Bilbao people there. There were no tourists or foreigners of any kind. I’d love to go back and see the changes.

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Guggenheim Museum, Bilbao. © Iker Gil.