Klusenstein castle was built in 1353 by Gerhard of Plettenberg, a vassal of earl Engelbrecht III of the Mark. The castle formed the boundary fortification of the earldom Mark to the bishopric state of Cologne and the earldom Arnsberg. All three territories met at the Hönne river valley, the castle was also overlooking an old road crossing the valley. During the feud between earl Engelbert and Gottfried IV of Arnsberg, the castle was under siege in 1366, but did not fall.
When the last earl of Arnsberg, Gottfried IV, sold the earldom to the bishop of Cologne, the castle lost its importance. Until the 17th century the family of Werminghausen owned the castle. During the 30 years war (1618-48) both Swedish and Hessian troops stayed in the castle. In 1695 the Brabeck family bought the castle, and was sold in 1812 to the Löbbecke family. In 1904 it was sold to the Hoesch company, and now belongs to the company Rheinkalk.
The castle is located on a 60m high cliff over the Hönne river valley, at around the narrowest part of the valley. At the bottom of the rock is a small cave in total 51m long. One corridor bends upward, but about 30m below the plateau it is blocked by stones. There were legends about a secret escapeway of the castle, in 2003 the top entrance to the cave was found below the eastern palais destroyed in 1840.
Below the castle is a mill, however though named Klusenstein mill it did not belong to castle. Since 1912 the railway connecting Balve and Menden runs directly below the castle.
The Externsteine (Extern stones) is a distinctive sandstone rock formation located in the Teutoburg Forest, near the town of Horn-Bad Meinberg. The formation is a tor consisting of several tall, narrow columns of rock which rise abruptly from the surrounding wooded hills. Archaeological excavations have yielded some Upper Paleolithic stone tools dating to about 10,700 BC from 9,600 BC.
In a popular tradition going back to an idea proposed to Hermann Hamelmann in 1564, the Externsteine are identified as a sacred site of the pagan Saxons, and the location of the Irminsul (sacral pillar-like object in German paganism) idol reportedly destroyed by Charlemagne; there is however no archaeological evidence that would confirm the site's use during the relevant period.
The stones were used as the site of a hermitage in the Middle Ages, and by at least the high medieval period were the site of a Christian chapel. The Externsteine relief is a medieval depiction of the Descent from the Cross. It remains controversial whether the site was already used for Christian worship in the 8th to early 10th centuries.
The Externsteine gained prominence when Völkisch and nationalistic scholars took an interest in the late 19th and early 20th centuries. This interest peaked under the Nazi regime, when the Externsteine became a focus of nazi propaganda. Today, they remain a popular tourist destination and also continue to attract Neo-Pagans and Neo-Nazis.