To be privately owned
Ringberg Castle

Ringberg Castle is a structure that rises halfway up the Ringberg in the Tegernsee Mountains. This castle in Bavaria, Germany, is known for its long construction period and artistic design.
History+
Construction of the castle began in 1912 under Duke Luitpold in Bavaria, a member of the Wittelsbach secondary line. He dedicated a large part of his fortune and sold other properties to finance the construction. Despite the long construction period until his death in 1973, only a few rooms were habitable. A special feature is the comprehensive artistic design by Friedrich Attenhuber, who not only created paintings and murals but also designed a large part of the furnishings.
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: 47.6792, 11.7497