The Ile de Haus was the headquarters of the Gestapo in Cologne between 1935 and 1945, and the building became a symbol of the Nazi era in the city, and aims to document the way in which the Gestapo dealt with people. In the basement of the building is one of the most well-preserved Nazi-era detention sites, with more than 1,800 inscriptions on the wall bearing witness to persecution, torture and murder.