To be privately owned
Château de Dourdan

In the town of Dourdan in the French department of Essonne stands the Château de Dourdan, a castle from the early 13th century. It was built as a royal fortress.
History+
The construction of the Château de Dourdan began at the start of the 13th century, commissioned by King Philip II Augustus. It replaced an older wooden structure. In 1385, the castle became the property of Duke Jean de Valois. During the Huguenot Wars, it served as a garrison for the troops of the Duke of Guise. The keep of the complex, an example of Philip Augustus's architecture, served as a royal prison until the 17th century. Notable prisoners included Joan of Burgundy and La Hire, a companion-in-arms of Joan of Arc.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Hervé Rebours
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: 48.5298, 2.0111