Scientists have pictures of huge lunar pits that they think are the entrances to lava tunnels on the moon. They say that, if these tunnels are not filled, they could provide passages for livable human lairs on the moon. They would create a perfect radiation shield and their could be some interesting minerals there.  https://www.google.com/amp/s/www.space.com/amp/moon-colonists-lunar-lava-tubes.html