To be privately owned
Schönstein Castle

In the Altenkirchen district, Rhineland-Palatinate, stands Schönstein Castle, a border house castle. It was first documented in the 13th century.
History+
The first written mention of Schönstein Castle dates back to 1255. From 1281, the complex served as a pledge object for the Archdiocese of Cologne. In 1589, Hermann von Hatzfeld-Werther was enfeoffed with the castle, which was already in poor condition at that time. The necessary maintenance costs were estimated at 16,000 guilders in 1594. During the Thirty Years' War, the castle suffered damage when it was plundered and set on fire by Swedish troops. However, it was rebuilt at the behest of Wilhelm von Hatzfeld.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Schloss_Sch%C3%B6nstein_2.jpg
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: 50.7768, 7.7506