What is a bunker?

Bunkers are concrete structures used to protect people from bombs and shells. The German bunkers were made of very hard concrete that was re-inforced. The walls were very thick to absorb the shock.

Atlantic Wall - Hitler fortified the northern coast of France in order to prevent the Allies from invading. This ring of fortification was called the Atlantic Wall. This consisted of all types of defenses but included concrete Bunkers for the soldiers who manned the guns and also bunkers that housed heavy artillery to fire on the attacking ships and soldiers.

Anti-Aircraft Towers - Large concrete towers were built around important industrial cities that the Allies tried to bomb. These Flak-towers were concrete and steel and included a bunker at the bottom and anti-aircraft artillery mounted on the top.

Vienna was the capital of Austria and the site of several important factories and air fields. Since it was a prime target the Germans ringed the city with anti-aircraft positions, including towers located throughout the city.