To be privately owned
Siersdorf Castle

The Commandery of Siersdorf is the ruin of a castle-like manor house in Aldenhoven-Siersdorf, North Rhine-Westphalia. Originally a settlement of the Teutonic Order, the current ruin shows destruction and reconstruction.
History+
The origins of the Siersdorf Commandery date back to 1219, when Count Wilhelm III of Jülich gifted the church in Siersdorf and its appurtenances to the Teutonic Order – a gesture of gratitude for care received during the Fifth Crusade. This established Siersdorf as the oldest order settlement of the Bailiwick of Alden Biesen. Between 1264 and 1267, the Kleine Hof was built as the first commandery building. In 1543, the complex suffered damage and looting during the Third Guelders War of Succession.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.wehrbauten.de/thread.php?threadid=570
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: 50.8999, 6.2221