Subterranean Muse

To find Berlin's most unusual art exhibition, jump off the tram at Alexanderplatz in the center of Berlin and duck down a flight of broad concrete stairs into the Underground station. Take a quick right, stop at a yellow, graffiti-covered steel door. Knock.

Nina and Torsten Römer, curators of Project Paradise, open the door and lead the way deeper into the earth along a narrow concrete passageway to a Nazi-era bunker. During World War II, Berlin's huddled masses sheltered here as Allied bombs flattened their city. Until Nov. 2, you're more likely to bump into Hitler, as played...