To be privately owned
Schweppenburg Castle

In the lower Brohl Valley near Brohl-Lützing in Rhineland-Palatinate stands Schweppenburg, a historic castle. Originally conceived as a medieval castle, it has been transformed several times and now presents itself as a Baroque palace.
History+
The first documented mention of Schweppenburg as a castle dates back to 1365. Twelve years later, in 1377, the complex, along with the Schweppenburger or Mosenmühle, came into the possession of Arnold von Schweppenburg, a juror from Andernach, as a fief of Electoral Cologne. Schweppenburg received its current Baroque appearance through reconstruction between 1637 and 1639 under the direction of Bertram von Metternich.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:Schweppenburg_2010.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: 50.4672, 7.3083