Rivière souterraine de Labouiche
The 19th longest cave in the world
10km · Length
The Labouiche underground river (French: Rivière souterraine de Labouiche) forms a long underground cavity concealing a prehistoric site dating back to the Magdalenian period. It is located 6 km northwest of Foix, in Ariège, France. It lies within the municipalities of Vernajoul and Baulou, and within the perimeter of the Ariège Pyrenees Regional Natural Park.
Cave data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).