The Grotte des Demoiselles
The underground cathedral the property is named after, 500 m away on foot.

This is the cave the property is named after, and it is 500 metres away. You can walk there from the courtyard, which, for a show cave of this scale, is genuinely unusual.
The Grotte des Demoiselles is one of the great developed caverns in France. You descend by a funicular cut into the rock, which replaced the old ladder descent and is already part of the experience. At the bottom, the main chamber opens into a volume long known as the cathedral: tens of metres of vault overhead, a floor that drops away, and a central formation that local tradition named the Virgin and Child.
The rest of the route runs through draperies, columns and organ pipes, lit with a restraint that has aged well. The visit is guided, takes about an hour, and follows a made-up path. The temperature stays constant at around twelve degrees year round: it is the ideal outing on a scorching afternoon, and you will want a layer even in mid-August.
The cave has a dense history. Long known to local people, it sheltered Camisards during the Cévennes wars, something the guides tell well, and which roots the visit in the region’s Protestant history rather than in geology alone.
For a group it is the perfect fallback: it works in the rain, it works with grandparents, it works with children, and it asks for no particular fitness beyond a few steps. Just check the seasonal opening times, and book ahead if there are a lot of you.