To be privately owned
Weissenegg Castle

On a steep ridge at the southern edge of the Graz Basin in the municipality of Mellach, Styria, stands Weissenegg Castle, with a history dating back to the 13th century. This castle is an example of the evolution from a fortified residence to a noble seat.
History+
The origins of Weissenegg Castle date back to the late 13th century, when Konrad von Thurn had a fortified residence called “Thürndl” built on this site. Between 1363 and 1456, this seat was a fief of the Counts of Cilli. In 1505, Jörg von Weissenegg took over the estate, and his family expanded the fortified residence into a castle, owning it until the 17th century. Subsequently, numerous changes of ownership followed until 1923. From 1923 to 1981, the castle belonged to the Counts of Trauttmansdorff.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Clemens Stockner / CC BY-SA 3.0 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: 46.9107, 15.4943