To be privately owned
Mitterau Castle

Mitterau Castle, a historic structure in Lower Austria, is an example of Baroque architecture. Originally built around 1600, it has been owned by the same noble family for over 300 years.
History+
The origins of Mitterau Castle date back to approximately 1600. A transformation, which gave the castle its current appearance, took place in 1754. Since 1710, the estate has been owned by the noble Montecuccoli family. Around 1740, Count Zeno Montecuccoli relocated the family seat from the nearby Hohenegg Castle to this location. During World War II, the castle suffered considerable damage.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Mitterau_Schloss.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: 48.2005, 15.4796