La Verna cave

La Verna is a show cave in the commune of Sainte-Engrâce in the department of Pyrénées-Atlantiques in France. 660 metres (2, 170 ft) of mined tunnel leads into the Salle de la Verna, the largest chamber in a show cave in the world. It has a diameter of 250 metres (820 ft), a height of 194 metres (636 ft), a surface area of 5 hectares (12 acres) and a volume of 3.6 million cubic metres (130, 000, 000 cu ft). A river cascades into the chamber from halfway up the east wall, and sinks into boulders near the base of the chamber. The chamber was named after the Lyon scouts, La Verna Troop, who helped in the attempted rescue of Marcel Loubens who died following a fall during the 1952 explorations. In 2003 a standard 4 person hot-air balloon was flown in Salle de la Verna.

Cave data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).