To be privately owned
Auenstein Castle

Auenstein Castle, a historic structure in the Swiss Canton of Aargau, evolved from a medieval castle. It stands on a rock and has been transformed from a ruin into a habitable castle.
History+
The origins of Auenstein Castle date back to the 13th century, when the Lords of Gowenstein presumably had a castle built. The complex was first documented in 1307 as property of the Lords of Rinach. During the conflicts between the Habsburgs and the Swiss Confederates in 1389, the castle was stormed and set ablaze by Bernese troops. For centuries, it remained a ruin, but due to the associated dominion over the village of Auenstein, it changed hands multiple times.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Auenstein_Schloss.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: 47.4153, 8.1396