One of the largest bunkers ever constructed, the Blockhaus was built under immense secrecy, utilizing unimaginable engineering feats, and was a potential gamechanger for Hitler at the tipping point in the war. Though the allies had no idea what secrets the building held, they knew they must destroy it. For months the Allies bombed Blockhaus and the Germans kept rebuilding it. Yet throughout the war and even after capture the Allies couldn’t figure out what new terror the Nazis were constructing inside. As the war wound down – the Allies finally uncovered the mysteries of the building and its potential devastating impact on the conflict.