It floats and it has a green wall. If you ask a casual visitor about the reasons for the success of the building, this is the answer you are going to get. If you ask a critic, the argument will probably include the folded landscape of the plaza, the sculptural space of the main staircase or the latticework of the cast iron roof. Both of them are right, and both in a paradoxical way. Some of these features are the result of a complex process, often beyond the control of the architects, and others are reinterpretations of discoveries made elsewhere. Besides, the building is sprinkled with minor avoidable or unavoidable snags: from the solemn section of the underground auditorium to the generic, windowless galleries or the small low-ceilinged restaurant at the top; the contrived circulation, which implies going one floor up and two down to reach the auditorium; not to speak of the puny water features, the unnecessary handrails in the plaza and the main stairs, or the crude weldings of the steel plates. And all things considered, the building is an unqualified success, with the crowds that fill it every day or with the architectural community, who has mutated its initial reticence into unanimous support...[+]