Occupied since prehistoric times, the site of this clifftop fortress commands an incredible view over the surrounding valley. Abandoned in the 17th century, it's an atmospheric place to wander – but is accessed by a winding, crumbling staircase, so take care as you hike up. Note that due to its exposed position, the fort is closed during heavy rain or high winds.
The path begins down in the valley, on the way to the Auberge des Seguins; signs show you the way, but ask anywhere in the village for directions.