Sainte-Baume
The sacred grotto of Sainte-Baume (Grotte Sanctuaire de la Sainte-Baume) is at the foot of a massif a little southeast of the small town of Plan-d'Aups-Sainte-Baume and it's not easy to visit.
The grotto or cave is a 45-minute drive southwest of the town of St. Maximin-la-Sainte-Baume or a bit longer if you're coming from Marseille, but you have to hike the last part, from the Dominican inn, Hostellerie de la Sainte-Baume, through the forest to the site itself and it is uphill.
Inside the cave itself is the main altar and the whole place seems very odd. Mary's relics (bones) have been relocated from here to Saint Maximin.