The Berliner Unterwelten Museum is located in a former air raid shelter at Gesundbrunnen underground station, which has been a protected monument since 1999. Visitors can explore the site on guided tours. On display are bunkers from the former government quarter, war rubble and archaeological finds as reminders of the Second World War. The exhibition also explores the difficult topic of military construction and historic preservation. At other sites in the city, Berlin Unterwelten also offers tours of otherwise inaccessible buildings such as the ruined flak tower in Humboldthain park, which was one of Berlin’s largest bunker complexes. With a surface area of 70 x 70 meters and a height of 42 meters, it was erected after Adolf Hitler ordered the planning and construction of flak towers in September 1940. Equipped with heavy anti-aircraft guns, the flak towers were supposed to protect Berlin’s city centre from bomb attacks. The tours of ‘the mother and child bunker’ in the former gasometer in Kreuzberg’s Fichtestraße also address the aerial warfare in Berlin during the war. In 1940 a six-story mother and child bunker with a three-meter thick ceiling was built into the old gasometer. During night-time bombing raids it initially offered a safe place to sleep for 6,500 mothers and children, but later as many as 30,000 people crowded into its interior. The permanent exhibition ‘Myth of Germania – Vision and Crime’ addresses Nazi plans for rebuilding the Reich capital and the accompanying crimes such as expulsions, deportations and forced labour. In November 2006 the Association won the ‘Silver Hemisphere’ for its historic preservation work, the highest distinction awarded in this field in the Federal Republic of Germany.