Humboldthain Flak Tower is one of three gigantic anti-aircraft towers built in Berlin in World War II. The dimensions of each tower were around 70 metres square with a height of 42 metres. On top were placed eight anti-aircraft guns and smaller calibre guns for low level defence. Associated with each gun tower (G-Tower or Gefechtsturm, literally Combat Tower) was a command tower known as the L Leitturm or Lead) Tower which provided guidance and control.
Construction of the tower was achieved in a remarkable six months, from October 1941 to April 1842. The walls were up to 2.5 metres thick and the ceiling almost 4 metres thick. Inside the tower were six levels of air-raid shelter accommodation for around 16,000 civilians. Some museum items were also stored within the towers.
After the war the inside of the tower was blown up by the Allies and the remains mostly hidden by the creation of an artificial hill of bomb rubble, After many years of clearance work by Berliner Unterwelten, the interior of the tower was made accessible for pre-booked visits.