Daylight. hikers climbing a path near a river towards the entrance to the cave across the bridge. The Bonheur Happiness River has its spring near the observatory Mont Aigoual at the border of the Cevennes. This area is not karstified, as it does not consist of limestone, and the river flows on the surface. After 6km it reaches the small karst area called Causse de Camprieu and immediately enters the underground. The river vanishes in a huge cave and forms a subterranean gorge. It reappears after 500m, and from there it is called the Bramabiau River. The cave was discovered in the 1888 by E. A. Martel.