The remains of the castle can be visited
Château de Montlhéry

The Château de Montlhéry, a castle ruin, rises in the French region of Île-de-France. The preserved keep shapes the silhouette of the complex, with a history dating back to the 10th century.
History+
The origins of the castle date back to the period between 991 and 1015. In the 11th century, a new fortress was built on the same site, which was later replaced in the 13th century by the complex still visible today. This younger castle is characterized by a pentagonal plan, with a large keep forming its point. A gate system protected the access on the opposite side. Historical research also suggests a possible second outer bailey and a chapel within the complex.
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: 48.6350, 2.2723