The Lanterne des Morts is a 12th-century cylindrical tower, about 15 metres high, that stands in the garden behind the cathedral. Its purpose is unknown. The most common theories are that a flame was lit at the top to guide souls of the dead, or that it served as a charnel tower where bones were stored after the surrounding graveyard reached capacity. Neither is proven.
The tower is one of only a handful of surviving examples in France, and Sarlat's is the best preserved. It cannot be entered, but the exterior in the quiet cathedral garden — away from the tour groups on the main square — is one of the more genuinely mysterious spots in the Dordogne.