Today's Flickr photo with the most hits: the House of Terror, in Budapest.
The building currently houses a museum. With grotesque symmetry, the address was used, in turn, by both the Arrow Cross (Hungarian Fascist party) and by the AVH (Communist Secret Police). It's a sombre place and merits a reflective visit. It's rare to have the opportunity to enter the heart of darkness - such buildings seldom survive.
The Prinz-Albrecht Palais in Berlin (HQ of the Gestapo and SS) was bombed into oblivion in 1945, leaving only its foundations. A very public argument about what to do with that site, and even when it was finally resolved not to use it for 'development', how to present the dark story associated with it, was carried on for a decade, in the newly re-united Berlin.
Preserving the opportunity for people to step into a extant basement, such as the one at 60 Andrassy Avenue, is vitally necessary. Without it, we risk walking towards a future where people are not given the option of visiting - they are simply taken to the basement.