It's a strange feeling to come into a dark, half-blasted bunker, see parts of stairways and cables hanging out of the wall and walk through rubble in between holes that go several meters down into the ground. It's eye-opening to crouch down in an air raid bunker and experience how it must have felt when the situation was for real.
These are just a couple examples of the unique experiences offered at Berliner Unterwelten (Subterranean Berlin). The museum offers tours of some of Berlin's most important underground structures, such as bunkers, abandoned subway stations, air raid shelters dating back to World War II and tunnels for smuggling people out of East Germany during the Cold War.
Berliner Unterwelten was founded in 1997 to explore, document and preserve the city's subterranean architecture. The organization's base is in a former air raid bunker in the Gesundbrunnen subway station, now a museum—the Unterwelten Museum (Subterranean Museum)—that offers various tours through Berlin's underground. The bunker was cleared and reconstructed by the group transformed into a museum while maintaining its original character. Hiding on four floors below Berlin are dozens of bunkers, tunnels, walkways, canals, the route of a pneumatic postal system, storage rooms, bomb and ammunitions storage, and abandoned subway stations.
Berlin, so full of history above ground, has a lot to tell in it's subterranean areas as well. There are exhibits about everything from air raid bunkers to the removal of rubble from the destruction during World War II. Berliner Unterwelten found a huge file system about slave workers during the war in a forgotten bunker, helped the former workers to receive reparation pay and have an exhibition about slave workers in Berlin. Found objects such as ammunition, grenades, gas masks, etc are on display as well. There is an exhibition about Hitler's "Germania," his utopian vision to rebuilt Berlin. (The exhibition shows that the project was not, of course, a utopia after all.)
Berliner Unterwelten also works to preserve subterranean areas. They have dug and cleared out many locations, including half destroyed bunkers, and opened them to the public. Several different tours are offered, including underground bunker hospitals, mother-and-child bunkers, flak bunkers, subterranean factories, examples of subterranean escape routes from East to West Berlin, Flak towers, an underground prison, Cold War bunkers for nuclear war and a tour through the Schwerbelastungskörper, a heavy tower built to test the possibilities of erecting Germania on the sandy ground of Berlin.