To be privately owned
Lanke Castle

In Wandlitz-Lanke, Brandenburg, stands Lanke Castle, a building in the French Renaissance style. Originally a baroque country house, it was transformed into a castle by Eduard Knoblauch in the mid-19th century.
History+
The first documented mention of Lanke dates back to 1315. After various owners, including the von Arnim and von Götze families, Field Marshal Otto Christoph von Sparr acquired the farms devastated by the Thirty Years' War and consolidated them into a manor. In the 17th century, a baroque manor house was built, which later came into the possession of the Counts von Redern. Around 1853, Count Friedrich Wilhelm von Redern commissioned architect Eduard Knoblauch to convert it into a castle. Knoblauch integrated parts of the old manor house, such as the cross-vaulted cellars, into his plans. The conversion was completed around 1859. In 1914, the great-grandson of Count von Redern sold the entire estate to the city of Berlin.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Schloss_Lanke_06.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: 52.7598, 13.5657