By Alice Scarsi A former Nazi bunker, built during World War 2 in the heart of Hamburg by hundreds of concentration camp prisoners, has been transformed into a stunning £50m luxury hotel. The Flak Tower IV bunker, situated in the St Pauli district, was one of two towers made by the Nazis for air defence. This huge building, which still stands tall in St Pauli’s skyline, once sheltered up to 30,000 residents from the Allies’ airstrikes under its 16.4-foot thick concrete roof. Constructed by over 1,000 forced labourers in just 300 days, this 131-foot tall grey structure was taken over by develop…