The Crypt of the Night Mother is a location in Bravil underneath the Statue of the Lucky Old Lady. It is only accessible during the Dark Brotherhood quest "Honor Thy Mother," whereafter the entrance is permanently sealed.
The Crypt is a circular cave, with stalactites and stalagmites and several pillars holding up the ceiling. Scattered around the room are four stone chests that contain leveled loot. Opposite the entrance is a raised altar flanked by four braziers. Upon the altar are the remains of The Night Mother. At the foot of the altar are five small skeletons, possibly the children the Night Mother sired with Sithis and then sacrificed to him.