La Verna cave

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.

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.

[5][6][7] Explorations still continue in this and in other systems within the extensive Pierre-Saint-Martin karst area where 13 underground rivers and a total of 288 kilometres (179 mi) of passages, chambers and shafts have been mapped.

[8][9] Most of the Gouffre de la Pierre-Saint-Martin is formed by dissolution in Cretaceous limestones, and the main river reaches a base level where it flows over insoluble schists of the Paleozoic basement rocks.

Since the opening of la Verna to visitors, in 2010, a team of researchers of the French national museum of natural history, under the leadership of Professor Arnaud Faille, closely follows their evolution.