To be privately owned
Stadeck Castle

In Stadecken-Elsheim in Rhineland-Palatinate, Stadeck Castle, a former moated castle, is located. Today, it is almost completely integrated into the town center.
History+
The construction of Stadeck Castle took place in 1276 by Count Eberhard I of Katzenelnbogen. The first documented mention of the complex dates back to 1291. In 1349, Counts Johann II and Eberhard IV of Katzenelnbogen made an agreement with Count Walram of Sponheim to finance construction work on the jointly owned castle. It subsequently became an important administrative center.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.wehrbauten.de/thread.php?threadid=899&sid=246e8c9fdbfa80ccf9a3497b2adfd6ed
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: 49.9115, 8.1358