Aven Armand is a single enormous cavern buried 100 meters beneath the Causse Méjean in Lozère. A funicular takes you down to a chamber large enough to hold Notre-Dame de Paris, where more than 400 stalagmites rise from the floor like a petrified forest. The tallest reaches 30 meters, making it one of the largest stalagmites ever recorded.
The 45-minute guided tour stops at eight viewpoints around the chamber, with sound and light effects that are tasteful rather than tacky. The highest platform gives a full overview of the stalagmite forest and is accessible to visitors with reduced mobility.
The cave is on the Causse Méjean, about 90 minutes north of Montpellier. The nearest village is Hures-la-Parade; the town of Meyrueis, a few kilometers further, has restaurants and accommodation. Open daily in summer, with reduced hours in spring and autumn. Closed in winter.