The former Stasi headquarters in Berlin – above – is one of the creepiest places I've ever visited. It's been mothballed, and now functions as a museum – not a very popular one, so after paying the lady at the door Helen and I were left to wander around the corridors, which still smell vaguely of cigarette smoke, alone.
The compound was also home to a large part of the Stasi's epic archive of informant material, a large amount of which was torn up – by hand – in the final days of the DDR. There's a fascinating article in Wired this month about the Fraunhofer institute's attempts to develop a computerised scanning system that can piece it all back together – to do so by hand would take 700 years.
The article is online here.