Lightness. Transparency. Long span. Tension. These are the elements which fascinate me as an engineer. There are a lot of structures which incorporate the first three - not very many where the greater part of the structure is pure tension. Bucky did some but my favourite by far is the group of cable-net structures for the 1972 Olympic Games in Munich. They are by architect Gunther Behnisch with Frei Otto and the engineers Fritz Leonhardt and Jorg Schlaicht. There are so many people involved because it was a competition which Behnisch won and was then surrounded by expert helpers.
Even today the sheer scale of the structure is profoundly impressive. It still gives me a thrill just to look at the photographs. I remember visiting the site during construction and being astounded at the size of the components, particularly the cast steel nodes for the stadium which were as big as a small room. The steel cables were twinned as a safety precaution - and to reduce the section size at the clamping points where they crossed over each other. There was this great net of cable clamped together on the ground waiting to be hoisted up the pylons.
Apart from the excitement of such large two-way curved structures, what really hit me was the audacity of the engineers and architects in proposing a structure for whose type and scale there was no precedent. At that time the analysis of this kind of structure was daunting. Otto and the Lightweight Structures lab did a lot of hanging-chain modelling along the lines of Gaudi. And then somebody came up with an early computer analysis. But even with our current advanced computing techniques it would still be a challenge. Everything had to be designed from scratch: gigantic compression masts, enormous top castings, cable junction castings and a variety of special cabled clamps. And there was that clever detail for attaching the glass cladding via rubber shock absorber mounts.
It's all still there, and when the re-cladding is completed I'm going back to see it again because there is something very special about transparency: it enables you to grasp the beauty of the structure from both inside and out.