To be privately owned
Gnemern Castle

Water Castle Gnemern, a historic structure in Mecklenburg-Vorpommern, was once built to protect trade routes. This complex, which is privately owned, is a rare example of an early Baroque country house that has largely retained its original form.
History+
Between 1218 and 1223, Prince Borwin initiated the construction of Water Castle Gnemern. Its strategic location served to protect the overland trade route connecting the cities of Rostock and Wismar. In 1661, the castle came into the possession of the von Meerheimb family, who held it until its expropriation in 1945. A fire in 1676 almost completely destroyed the complex. From 1682 to 1685, it was rebuilt in the form of a new manor house.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Roland Neubert, Halle (Saale)
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: 53.9319, 11.8327