To be privately owned
Ruhreck Manor

Haus Ruhreck, a manor house and estate, is located in the Boele district of Hagen in North Rhine-Westphalia. Originally built as an entrepreneur's villa in the style of a castle, it is an example of historical architecture in the region.
History+
The construction of Haus Ruhreck took place in 1878, commissioned by the manufacturer Caspar Diedrich Killing, owner of the Killing & Söhne wagon factory. He named the estate Killingsburg. Following his divorce from his wife, who came from the Ziegenbein family, the house passed into her ownership. It was subsequently renamed Haus Ruhreck and remains in the possession of the Rempke community of heirs to this day.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.wehrbauten.de/thread.php?threadid=861
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: 51.3889, 7.4582