To be privately owned
Klusenstein Castle (Deilinghofen)

Klusenstein Castle, a hilltop castle, stands on a 60-meter-high cliff at the edge of the Hönnetal in Deilinghofen. Built in the 14th century, it once served as a border fortification.
History+
The origins of Klusenstein Castle date back to 1353, when it was constructed by Gerhard von Plettenberg on behalf of Count Engelbert III of the Marck. Its strategic location made it a stronghold on the border between the County of Marck, Electoral Cologne, and the County of Arnsberg. During a conflict between Count Engelbert and Count Gottfried IV of Arnsberg, the castle successfully withstood a siege. However, after the sale of the County of Arnsberg to the Bishop of Cologne, Klusenstein lost its military significance.
Source: Wikipedia · Licence: CC BY-SA 4.0
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 51.3810, 7.8512