This was a German major construction project (1943/45).
The project comprised seven underground structures in the Eulengebirge and the Schloss Fürstenstein and Jedlinka Palace in Lower Silesia. None of these works was completed, and all survive in different states of completion with only a small percentage of their tunnels reinforced by concrete.
The purpose of the project remains uncertain because of lack of documentation. Some sources have suggest that all the structures were part of Hitler’s headquarters, but others that they were a combination of headquarters and weapons manufacturing facilities. Comparison with similar facilities suggest only that the castle was adapted as a headquarters or other official residence, and that the tunnels in the Eulengebirge were planned as a network of underground factories.
The construction work was done by forced labourers, prisoners of war and inmates of concentration camps, very many of whom died as a direct result of mistreatment, disease and malnutrition.
As the size and frequency of Allied heavy bombing increased, and the efficiency of the bombing improved, the German leaderships decided to relocate a large part of its strategic armaments production into safer regions, including the Sudetenland. The German plans to protect critical infrastructure elements also involved transfer of weapons factories to underground bunkers and the construction of major air raid shelter complexes for government officials.
In September 1943, Albert Speer, the minister of armaments and war production, and the senior management of the Organisation 'Todt' began to discuss the 'Riese' project. As a direct result, the Schlesische Industriegemeinschaft A.G. (Silesian Industrial Company) was created to undertake the required construction. In November camps were established for forced labourers, most of them from the German-occupied parts of the USSR and Poland, prisoners of war from Italy, the USSR and later from Poland after the defeat of the Warsaw Rising.
A network of roads, bridges and narrow-gauge railways was created to connect excavation sites with the nearest railway stations, and prisoners were set to work loading building materials, cutting trees, digging reservoirs and drainage ditches, and creating small dams on streams to supply water and remove sewage. Shafts and then larger tunnels were driven and blasted into the rock of the mountains, and the resulting caverns were reinforced by concrete and steel. For this purpose mining specialists were employed, most of them Germans, Italians, Ukrainians and Czechoslovaks, but the most dangerous and exhausting work was done by the prisoners.
The tunnel-driving progress was slow because the rock of the Eulengebirge is hard gneiss. Similar facilities were bored more easily in soft sandstone, but the harder and more stabile rock of the Eulengebirge offered the advantage of total protection from Allied air raids and possibility of building underground halls with a height of 39 ft 4 in (12.0 m) and 64,585 cu yards (6000 m³).
In December 1943 there was a typhus epidemic among the prisoners, which was almost inevitable given the fact that they were held in totally unhygienic conditions at five camp complexes, and were both exhausted and starving. As a result, construction slowed significantly despite the large but unknown number of forced labourers and prisoners of war working on the project, some of them right to the end of the war. Also unknown is the number of impressed labourers and prisoners who lost their lives.
As well as those at Schloss Fürstenstein and the palace at Jedlinka (Tannhausen), the other projects were those of the Rzeczka-Walim (Dorfbach-Wüstewaltersdorf), Włodarz (Wolfsbeg), Osówka (Säuferhöhen), Sokolec (Falkenberg), Jugowice (Hausdorf), Soboń (Ramenberg) and Głuszyca (Wüstegiersdorf) complexes.