To be privately owned
CastleBonn - Friesdorf
Friesdorf Castle

Burghaus Friesdorf, with origins dating back to the 12th century, is one of the oldest residential buildings in the Rhineland. It is characterized by its walls, up to two meters thick, resting on a basalt foundation.
History+
The history of Burghaus Friesdorf begins in the 12th century, when it likely served as the noble seat of the Knights of Friesdorf. This family was first documented in 1139 and last mentioned in 1328. Originally known as Turmhof, the complex included not only the residential building but also outbuildings, as well as the old Friesdorf church, which stood there until 1888, and an adjacent cemetery.
Image: http://www.wehrbauten.de/thread.php?threadid=842
Location: 50.6954, 7.1235