The Dark Worlds and the Bunkers, Subways & the Cold War tours are organised and sold by Berliner Unterwelten.
The Dark World tour goes through an air shelter from the World War II under the train station at Gesundbrunnen.
The Bunkers, Subways & the Cold War tour goes through two fallout shelters from the Cold War. The focus of the tour is about what would have happened if the Cold War turned into World War III.
You can read more about Berliner Unterwelten on Atlas Obscura.
Read about the tours on the Berliner Unterwelten website, where you can also book tickets for a guided tour.