The subterranean world of Berlin

Darkness, cold, humidity …anyone tempted? No? Of course, not a lot of Berliners and tourists would be willing to pay for that, but never trust appearances: this could be the experience of a lifetime!
The “Berliner Unterwelten eV” (the society for the exploration of the subterranean Berlin) organizes underground guided tours of the city since 1987; [...]