Adlerhorst (Eagle's eyrie) was a World War II bunker complex in Germany, located within Kransberg Castle (incorporated into Usingen in 1971), Wetterau in the Taunus mountains in the province of Hesse.
Designed by Albert Speer as Adolf Hitler's main military command complex, it was reassigned by Hitler in February 1940 to Luftwaffe chief Hermann Göring as his headquarters for the Battle of Britain, later serving as the Fuhrer's only during the 1944/5 Ardennes Offensive.
Pre World War 2, there were no official Führer Headquarters, with Hitler using either existing military complexes, or mobile facilities close to the battle lines. Under plans developed by Martin Borman and planned by Speer, a series of Führer complexes were built, the best known of which were: the Führerbunker in Berlin; the Berghof complex in Berchtesgaden, Bavaria; and the Wolfsschanze near Kętrzyn in modern day Poland.
Austrian noble Emma von Scheitlein acquired Kransberg Castle in the village of Ziegenberg in 1926, and used it for society events. Chosen due to its central location as the proposed main military command headquarters of Hitler, it was appropriated by the Nazi government in 1939. Speer immediately began adapting it, designing military-grade infrastructure which was well disguised and adapted to fit-in with its surroundings.