To be privately owned
Thorn Castle (Palzem)

In the district of Schloss Thorn in Palzem, Rhineland-Pfalz, stands Schloss Thorn, a complex that emerged from a former castle. It stands on a hill that controls access to the Moselle Valley and the Saargau, marking the southwesternmost point of the Trier-Saarburg district.
History+
The origins of the castle lie in a medieval fortress, presumably rectangular in design and fortified with round corner towers. This castle was a fief and remained in the possession of the Lords of Bübingen, who were also hereditary marshals of Luxembourg, until the 16th century.
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: 49.5517, 6.3831