At first it stood as a defense against Allied bombs. In the 1950s it was used to store imported fruit from Cuba, and in the 1990s it became the location for the hottest techno-parties around. On Thursday an old Berlin bunker revealed its latest transformation: It now houses a private collection of contemporary art.

Walking through the massive five-storey concrete bunker that houses the Boros Collection on Reinhardstrasse in Berlin, you wouldn't guess that it had a far more sinister past. Back in 1942 Nazi architect Albert Speer built the place to help the city sustain what he believed would be the final blowout battle leading to a German victory. It was part of his and Adolf Hitler's grand "Germania" (more...) vision, whereby Berlin would be entirely renewed -- fully devoid of degenerate art, of course -- after the Germans had triumphed.

But today the old pock-marked fortress belongs to Polish-born collector and advertising entrepreneur Christian Boros and his wife Karen. And it was here on Thursday that they unveiled their impressive art collection that they've amassed over nearly two decades. Now the spiciest of international contemporary art sits in a cavernous piece of Berlin's architectural past. "This building is a landmark, a part of German history," Boros says. "It's not the Brandenburg Gate, but it has seen Berlin change a lot over the last half century."