Extensive construction work on a number of underground shelters and tunnels took place in the Owl Mountains (a part of the Giant Mountains) between 1943 and 1945. The exact purpose of these facilities remains unclear even today. German sources suggest that they were supposed to be turned into a huge underground shelter covering more than 35 square kilometres, with one of Adolf Hitler’s Führer Headquarters at its centre. Furthermore, it was planned to be used as a refuge for the leading members of the military as well as a safe place for certain industrial facilities. The construction work was done by forced labourers from concentration camps. In this case, they came from the KZ Groß-Rosen. They were housed in a number of Außenlagern (subcamps or satellite camps) called "AL Riese” in the immediate vicinity to the tunnels and other construction sites related to the “Complex Riese.”