The mysterious Stasi interrogation 'prison' at Berlin-Hohenschönhausen, Berlin, Germany.

The Berlin-Hohenschönhausen Memorial is a gem of a place to visit if you are into history, espeicially in the 20th century and Cold War Germany.
I would recommend watching 'The Lives of Others' to get an idea of what the Stasi did here (and what Cold War East Berlin was like).
Unfortunateley they do not permit filming on the tour but I hope this video piques your interest and encourages you to visit.
I use the term 'prison' but really Hohenschönhausen was a processing and interrogation facilty. People did not come here to serve a prison sentence, they came here after being picked up by the police for interrogation and to either admit their crimes or spill the beans on their friends/work mates or even their own family.
GPS for entrance: 52.54190, 13.50013
Directions: S41, S42, S8 or S85 to Landsberger Allee. Change to tram M5 heading NE to the Freienwalder Str stop. Head down Freienwalder Str to the Prison.