The city’s former Gestapo HQ has been transformed into a museum tracing the roots and progress of National Socialism in Cologne from the foundation of the National Socialist German Workers Party in 1921 through to the liberation of the city by US troops on March 6, 1945. The former cells in the basement now form the main part of the exhibition, with the rest of the building given over to archives and research. One of the best-preserved prisons of its kind in the country, a visit here is a necessary part of any itinerary to the city.