In 1934, Jewish gold and jewelry merchant Leopold Dahmen began to built himself an impressive living-cum-office building right in the centre of Cologne, named after his initials in German spelling. Only one year later, he was expropriated by the Gestapo, the secret police of the Nazis, who then moved in here – and promptly began to construct cells in the basement. Over the next ten years this building remained in the hands of the Gestapo, who not only crammed up to three dozen prisoners into cells meant for 4 to 6 people later in the war, but also set up a guillotine in the backyard with which they executed almost 800 people over the years. Strangely, the building survived the Allied bombing campaign almost unscratched and was liberated by American troops in March 1945.

Turning a place of horror into a place of memory, the city now houses its own National Socialist documentation center here, with a permanent exhibition on the history of the building and the chance to visit the cells in the basement, where prisoners scratched messages like ‘If no one thinks of you, your mother will’. There is also a research center and a changing exhibition on topics associated with the 3rd Reich. A sobering place, but one that remains immensely important these days.