The caves, discovered in1819, have 5,200m of galleries on 5 floors, sparkling with a veritable treasure naturally sculpted in rock: stalagmites, stalactites, pendants, hangings and columns. The tour is done on foot, by boat or on a small train. A pilgrimage site since the 15C, the Sanctuary of Bétharram is remarkable above all for its Chapel of Our Lady with a (17C) Baroque décor, vast conventual buildings and Stations of the Cross with bas-reliefs painted by Alexandre Renoir (1845).