Today’s mountain stage took us into the town of Foix before heading up the Prat d’Albis. Foix, the hometown of French canal engineer Charles de Freycinet, sits upon the Ariège River, a tributary of the Garonne. But just northwest of the town lies an underground river, the Labouïche.
The Labouïche sits within a large cave system and is navigable for around 1500 meters, making it the longest navigable underground river in Europe. It was discovered in 1908 by Jules Dunac who, along with his two sons and a couple of young army officers, followed a stream known as the Fajal into the Aïgo Perdent, the Lost Water. Their exploration was taken up by pioneering speleologists Édouard-Alfred Martel in the 1910s and Norbert Casteret in the 1930s, who revealed the currently known extent of the river.
The river terminates in a siphon, a permanently submerged chamber that must be dived to pass. No one has so far managed to cross that siphon. In 2015, Franck Bréhier tried and managed to pass about 100 meters into the siphon before he was forced to turn back.