To be privately owned
Trostburg Castle
In the Swiss canton of Aargau, Trostburg Castle, a small fortress, stands on a rocky outcrop above the village of Teufenthal. Originally a medieval stronghold, it was transformed into a residential castle around 1750 and remains in private ownership to this day.
History+
The origins of Trostburg Castle date back to the 12th century when it was built by the Lords of Trostburg, first documented in 1241. As ministeriales of the Counts of Kyburg, they served the Habsburgs from 1264. A branch of the family later founded the nearby Liebegg Castle. After the extinction of the Trostburg line, the castle passed to the Lords of Rinach in 1346, who established a small dominion with lower jurisdiction over several surrounding communities. With Bern's conquest of Aargau in 1415, the Rinachs' power waned.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Trostburg_in_Teufenthal.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: 47.3304, 8.1185