Not sure if it counts as geek-oriented but take a look at the guided tours by Berliner Unterwelten [1]. They are really good. (Tours in English are available)

Not sure if it counts as geek-oriented but take a look at the guided tours by Berliner Unterwelten [1]. They are really good. (Tours in English are available) [1] https://www.berliner-unterwelten.de/en/index.html https://www.berliner-unterwelten.de/en/index.html