Mittelwerk was a German World War II factory built underground in the Kohnstein to avoid Allied bombing. It used slave labor from the Mittelbau-Dora concentration camp to produce V-2 ballistic missiles, V-1 flying bombs, and other weapons.

The Kohnstein is a hill in Thuringia, Germany, 2 kilometres southwest of the village of Niedersachswerfen and 3 kilometres northwest of the centre of the town of Nordhausen. Gypsum mining created tunnels in the hill that were later used as a fuel/chemical depot and for Nazi Germany factories, including the Mittelwerk V-2 rocket factory that used Mittelbau-Dora slave labour.