Riese [ˈʁiːzə] (German for “giant”) is the code name for a construction project of Nazi Germany in 1943–1945, consisting of seven underground structures located in the Owl Mountains and Książ Castle in Lower Silesia, previously Germany, now a territory of Poland.
None of them were finished; all are in different states of completion with only a small percentage of tunnels reinforced by concrete.
The purpose of the project remains uncertain because the lack of documentation. Some sources suggest that all the structures were part of the Führer Headquarters; according to others, it was a combination of headquarters (HQ) and arms industry but comparison to similar facilities can indicate that only the castle was adapted as an HQ or other official residence and the tunnels in the Owl Mountains were planned as a network of underground factories.
Due to increasing Allied air raids, Nazi Germany relocated a large part of its strategic armaments production into safer regions including the District of Sudetenland. Plans to protect critical infrastructure also involved transfer of the arms factories to underground bunkers and construction of air-raid shelters for government officials.
In September 1943, Minister of Armaments and War Production Albert Speer and the senior management of Organisation Todt started talks on Project Riese. As a result, the Schlesische Industriegemeinschaft AG (Silesian Industrial Company) was created to conduct construction work. In November, collective camps (Gemeinschaftslager) were established for forced labourers, mainly from the Soviet Union and Poland, POWs from Italy, the Soviet Union, and later Poland as an aftermath of the Warsaw Uprising (List of camps).
A network of roads, bridges, and narrow gauge railways was created to connect excavation sites with the nearby railway stations. Prisoners were reloading building materials, cutting trees, digging reservoirs and drainage ditches. Small dams were built across streams to create water supplies and sewage systems. Later the rocks of the mountains were drilled and blasted with explosives and the resulting caverns were reinforced by concrete and steel. For this purpose mining specialists were employed, mostly Germans, Italians, Ukrainians, and Czechs but the most dangerous and exhausting work was done by prisoners.
The progress of digging tunnels was slow because the structure of the Owl Mountains consists of hard gneiss. Most of the similar facilities were bored in soft sandstone but harder, more stable rocks gave the advantage of total protection from Allied air raids and the possibility of building 12 m high underground halls with a volume of 6,000 m3.
In December 1943, a typhus epidemic occurred amongst the prisoners. They were held in unhygienic conditions, exhausted and starving. As a result, construction slowed down significantly. There were at least five collective camps and an unknown number of forced labourers and POWs worked for the project, some until the end of the war. It is also undetermined how many prisoners lost their lives.