He has built the new Imperial War Museum in Manchester, England. He is sthe author of "The Spiral", a famous (so far unbuilt) design to extend the Victoria and Albert Museum in London. He has a Jewish Museum in San Francisco, a university in Mexico, a very large commercial development in Switzerland underway. How did it happen? How did he get from there - the promising young concert pianist - to here, one of the world's leading architects? As always with Libeskind, it was intellectual stimulation that he craved. In the end he did not see endless performances of works by others - creative performances, certainly, but with inevitable flaws - as sufficiently engaging. He turned instead first to the study of mathematics, then to architecture. He does not play the piano any more, though he listens to music and sometimes presents sketches for projects on lined music paper. And anyway, he never really quit the stage. "So much of what you have to do in architecture is performance," he told me once. "Not just the way you have to present your ideas, but the way the buildings themselves perform."

He went into teaching architecture, at Cooper Union, Harvard, Yale, London's Architectural Association. His own fantastical designs marked him out as a "paper architect", one for the cognoscenti, certainly not anyone who was ever going to build. He became a citizen of the world: it is not surprising that Americans think he is American and Germans German. And then, in 1988, he won the international competition to build the Jewish Museum in Berlin, a project that was to take 12 years to bring to fruition. Moving to Berlin, given his family background, was the hardest decision he ever had to make. But it proves that when Danny decides he is going to set out to achieve something, nothing will stop him. It's to do with being from a working class background, he once remarked. Architecture is primarily a middle-class profession with cultural pretensions. Libeskind and relatively few others -Britain's Lord Foster is another rare example- come from a different mindset. They want to win and they see no value difference between high culture - art galleries - and low culture - shopping centres. As Danny (who designs both) points out, they are both used by people.

So now what? How much of Libeskind's vision will be built? At worst, none of it. More realistically, only parts of it - and his proposed necklace of crystalline towers is the most vulnerable aspect in New York's current property slump. This was a competition for workable ideas, not for an immediately buildable scheme. The owners - the New York Port Authority - and leaseholder of the site, Larry Silverstein, are under no obligation to hire the winning architect. They could rebuild the vanished square footage however they liked. But that is not going to happen. Danny and Nina are looking for an apartment in New York. Their office there will be up and running soon. He is not, you may be absolutely sure, going to let this one slip through his fingers.