To be privately owned
Gudenau Castle (Villip)

Gudenau Castle, a two-part moated castle, is located near Villip in the Rhein-Sieg-Kreis. Its origins date back to the early 13th century, but it acquired its current appearance primarily in the 17th and 18th centuries. Its unique, terraced Baroque garden remains the only private garden of its kind in the Rhineland.
History+
The construction of Gudenau Castle is dated to the early 13th century. Around 1560, the four-winged main castle underwent extensive expansion, being fitted with a Gothic oriel and curved gables at that time. The castle's appearance developed in the 17th and 18th centuries. In the 17th century, the garden was also laid out in three terraces, incorporating Italian design elements. Until about 50 years ago, the castle was owned by the Neven du Mont family before passing to the Counts of Strasoldo.
Source: Wikipedia · Licence: CC BY-SA 4.0
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: 50.6341, 7.0865