Nassau Castle in Rhineland-Palatinate by EuroTourData
Nassau Castle is the restored ruins of the hilltop castle, built around 1100 as the tower house and expanded in 1124 as the fortified residence of the House of Nassau. In the first half of the 14th century, the pentagonal keep 33 meters high was built, which can be seen today as the butter-churn tower.
Since 1965, Nassau Castle has been taken over by the Rhineland-Palatinate General Directorate for Cultural Heritage (in German Generaldirektion Kulturelles Erbe Rheinland-Pfalz).
Source
The article Burg Nassau of German Wikipedia.

Image copyright info
© Creative Commons: Nassau Luftbild 071, author Fritz Geller-Grimm. License: CC BY-SA 3.0. Cropped from original.