Potsdam KGB Prison
After the war, the Soviet Security Service, KGB, established a prison on Leistikowstrasse 1 in Potsdam. In the fifties, between 900 and 1200 people were arrested. Few of them are known by name. Between 1954 and 1983 only Soviet military personnel were imprisoned. The prison closed in the mid-eighties and functioned as storage room until 1994 when the Russians handed over the building to German authorities.
Current status: Preserved with museum (2008).
Address: Leistikowstrasse 1, 14469 Potsdam.
Get there: Car.
Follow up in books: Andrew, Christopher: The KGB (1990).
Seems to be a reasonably large museum that can be combined with the nearby museums Lindenstrasse 54 and Schloss Cecilienhof. When I visited the prison in 2008, however, it was not yet open to visitors.