To be privately owned
Stein Castle

In Stein an der Traun in the Bavarian district of Traunstein is Burg Stein, a cave castle. It is considered one of the most significant complexes of its kind in Germany.
History+
The origins of the main castle are not fully clarified, with a presumed origin in Roman or Celtic times. The first documented mention of Burg Stein occurred in 1135. For centuries, the Törring family shaped the estate, owning it from the 13th century until 1633. Family members such as Albert von Törring-Stein and Adam Lorenz von Törring-Stein held the office of Bishop of Regensburg. In 1633, ownership transferred to Count Carl Fugger von Kirchberg.
Source: Wikipedia · Licence: CC BY-SA 4.0
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: 47.9879, 12.5476