To be privately owned
Neudenstein Castle

On a rocky outcrop above the northern shore of the Völkermarkt reservoir in Carinthia, Austria, stands Neudenstein Castle, a historic defensive structure.
History+
The origins of Neudenstein Castle date back to 1329, when it was built under Konrad von Aufenstein. Parts of the walls of the south and east wings from this early construction phase are still preserved. Following an uprising by Konrad's descendants, the castle fell to the Carinthian dukes in 1368, who granted it to various loyal followers, including the Himmelberger, von Graben, Plumegger, Windisch-Graetz, Kemetter, and Mandorff families.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.wehrbauten.at/ktn/kaernten.html
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: 46.6452, 14.5861