To be privately owned
Katzenelnbogen Castle

On a rocky plateau above the town of Katzenelnbogen in the Rhein-Lahn district of Rhineland-Palatinate stands Katzenelnbogen Castle. It is the origin and namesake of the Count's family of Katzenelnbogen.
History+
The castle's origins date back to 1094, when Vogt Diether I and his son Heinrich I began construction on the Vogt's estate of Bleidenstadt Monastery. Heinrich II, who grew up here, was elevated to the rank of Count by King Konrad III in 1138. In 1260, the House of Katzenelnbogen was divided into an older and a younger line. The original castle complex was completely rebuilt in 1371 under Wilhelm II. After the extinction of the Counts of Katzenelnbogen in 1479, the Landgraves of Hesse took over the rule.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://www.wehrbauten.de/thread.php?threadid=932
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: 50.2681, 7.9765