L'Hypogée des Dunes is an underground chapel in Poitiers, France. The chapel is one of the few surviving structures from Merovingian times. The chapel has a tomb containing approximately 35 burials.
Wikipedia https://en.wikipedia.org/wiki/Hypogée_des_Dunes
Address 109 Rue du Père de la Croix, Poitiers 86000, France
Coordinates 46°34'31.983" N 0°21'33.228" E