Notre-Dame-sous-Terre (Our Lady Underground) is a pre-Roman church with double naves, each terminated by two small sanctuaries. It was not rediscovered until the end of the 19th century, having been buried under later buildings. The architect Yves-Marie Froidevaux (1907-1983) cleared it by destroying the retaining wall. The church remains as close as possible to the original cave built by Saint Aubert, near which it was erected to welcome the increasing number of pilgrims.