Receiving vaults were used as a temporary burial site while an elaborate mausoleum or under ground crypt was being constructed to house the remains. Occasionally they were used to temporarily bury the remains of an individual until a decision was made regarding a permanent place of burial, or until the family had the funds to arrange for a permanent place of burial. (Wikipedia)
Most likely this building was used for temporary storage, this is the south.
Old New England cemeteries had temporary areas built into the side of a hill, or down under a large mound.
Inside is larger than I had thought. Also not a place I had ever considered photographing.