To be privately owned
Scharnhäuser Castle

In Ostfildern-Scharnhausen in Baden-Württemberg, the Scharnhäuser Schlössle, a small castle, is located. It was once built as a retreat for Duke Carl Eugen.
History+
Duke Carl Eugen of Württemberg had the Scharnhäuser Schlössle built in 1784 to find peace away from government affairs. The name “Carolus Otio,” engraved above the triangular gable, indicates this desire. Court architect Reinhard Ferdinand Friedrich Fischer designed the building in the classical style. An English garden was created around the Schlössle, modeled after Wörlitz Park, complete with artificial hills, water features, and a walkable island. An artificial ruin and a grotto were also part of it.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:SchlossScharnhausen.jpg
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Location: 48.7105, 9.2602