Going underground: who’s behind Berlin’s secret subway bedrooms?

There's actually an organization that specializes in tours of Berlin's underground architecture and offers some interesting guided tours (although they probably wouldn't include the subway bedrooms): http://berliner-unterwelten.de/home.1.1.html

When I first saw that, I was like... I wonder if that was a porn studio that they setup to avoid laws/taxes.

The front garden tableau (in a publicly accessible area): https://www.facebook.com/BerlinWriters/posts/978227365587788

The headline sounds like there are many of them, but these are the only two.

Does anyone have any sense if squatters ever hide elaborate rooms/false walls in public spaces? I've always been fascinated by this...