Flakturm IV or Flak Tower IV, a former Nazi bunker in Germany, will now be turned into a luxury hotel. In response to Berlin air-raids by Allied Forces in 1940, the Nazi regime issued an immediate decree to build air-raid shelters in cities all across the Third Reich. The Hochbunker in the St Pauli district of Hamburg was built during World War II and was one of two towers created by the Nazi&rsquos for air defense during the war.