To be privately owned
Grimnitz Castle

The Grimnitz Castle Ruin in Joachimsthal is a Romanesque border fortification of the Ascanians. Originally used as a hunting lodge, it secured routes and later served as a site for a glassworks.
History+
The first documented mention of Grimnitz Castle dates back to 1297, but historians assume it existed earlier under the Ascanian Margraves Johann I and Otto III of Brandenburg. It served as a hunting lodge in the Schorfheide and secured the road between Lake Werbellin and Lake Grimnitz, which led towards Uckermark and Pomerania. After the division of inheritance, the castle fell to the Johannine line and became the hunting residence of Otto IV and his successors up to Waldemar the Great. From 1340, the complex fell into disrepair, but was restored in 1514 under Elector Joachim I and modernized by Caspar Theiss. An event was the signing of the inheritance treaty between Brandenburg and Pomerania in 1529 at Grimnitz.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:BurggrabenRuineGrimnitz.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: 52.9782, 13.7593