hmm now I know where the cave dogma comes from catholic
The stable where Mary and Joseph spent the night of Jesus’ birth was most likely much like the cave at the shepherd’s field. That cave is beneath the Church of the Nativity, which was first built around AD 327 by Constantine the Great and his mother St. Helena to honor the birth of Our Lord. This cave is accessible to pilgrims by stepping down a short set of stairs to a grotto beneath the altar of the main sanctuary of the church. A metal star surrounded by marble slabs marks the spot of the blessed event, but in other parts of the grotto, the cave walls are still visible, although covered with tapestries in most places.