Cologne's Third Reich history is poignantly and exhaustively documented in the NS Documentation Centre housed in the very building that served as the headquarters of the local Gestapo (Nazi secret police). The basement prison, where scores of people were interrogated, tortured and killed, is now a memorial site.

　　Inscriptions and drawings on the cell walls offer a gut-wrenching record of the emotional and physical pain endured by inmates. The execution grounds in the courtyard are also part of the memorial. An audioguide may be rented for €2.