Bétharram caves
The Grottes de Bétharram (French pronunciation: [ɡʁɔt də betaʁam]) are a series of French caves located at the border of the Pyrénées-Atlantiques and Hautes-Pyrénées departments and of the Nouvelle-Aquitaine and Occitanie regions. Located near Asson, Lestelle-Bétharram and Saint-Pé-de-Bigorre, they offer a threeway discovery: by foot, by boat and finally, by train, the key to similar cave formation. The entrance is located in Asson and the exit in Saint-Pé-de-Bigorre.
Cave data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).