To be privately owned
Friedberg Castle

The Friedberg Castle Ruin, a former hilltop castle, was transformed into a residential building in the 20th century. It is located above the town church of Oppenau in the Ortenau district.
History+
The origins of Friedberg Castle likely date back to the 13th century, when it was built by the administrators of Allerheiligen Monastery. In the 14th century, ownership changed, and the castle came under the rule of the Bishops of Strasbourg. The original complex was a rectangular structure, whose feature was a round, elongated keep that also served as a residential tower. It was surrounded by two large neck ditches, which are now covered by modern development.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Public domain via Wikimedia Commons
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: 48.4767, 8.1675