To be privately owned
Osthoff Manor

Haus Osthoff in Dülmen is a historic manor and estate house, considered the oldest building in the city and the sole remnant of the former Osthoff knightly estate.
History+
Baroness Anna Maria von Landsberg acquired the estate in 1727 and is regarded as the builder of the manor house. The brick building represents the Baroque style of the 18th century and features an unusually high cellar with a cross-rib vault. Before World War I, Haus Osthoff was an excursion destination, surrounded by a garden and high forest. After World War II, it served as a private residence until the 1960s, but subsequently fell into disrepair as a protected ruin.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://de.wikipedia.org/wiki/Datei:D%C3%BClmen_-_Haus_Osthoff.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: 51.8349, 7.3039