To be privately owned
Welsbach Castle

On the southern slope of the Osselitzenberg in Carinthia is Welsbach Castle, a structure from the late 19th century. It is characterized by its design, modeled after French Renaissance city palaces, and is surrounded by a park with outbuildings.
History+
The construction of Welsbach Castle took place between 1898 and 1900 for the industrialist Carl Auer von Welsbach. The plans for the building were created by architects Anton and Josef Bierbaum. Previously, the Villa Marienhof, which served as a summer residence for the Viennese operetta singer Marie Geistinger, stood on this site. She sold the property to Auer in 1893, who resided in the castle until his death in 1929. To this day, it remains in the possession of his descendants.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Moelbling_Rastenfeld_Schloss_Welsbach_2012-10-18_CLX.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: 46.8581, 14.3898