To be privately owned
Eschelberg Castle

In Austria's Mühlviertel region, Eschelberg Castle is a historic structure that transformed from a medieval fortress into a Renaissance palace. Situated on a ridge in St. Gotthard-Eschelberg, it combines architectural elements from various eras and remains in private ownership to this day.
History+
The origins of Eschelberg Castle date back to 1205, when a castle under its owner, Hainricus de Esilberch, was first documented. Feudal sovereignty changed hands multiple times, from the Bavarian Counts of Leonberg to the Diocese of Passau, and eventually to the Austrian sovereign.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Schloss_Eschelberg-1.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: 48.3822, 14.1178