When I was growing up on Molokai, my Hawaiiana teacher told us that she knew of an extensive system of lava tubes. One was used by Father Damien to travel from the leper settlement to a church on the front side of the island. She mentioned that a lot of them were not safe because of a lack of fresh air. She also mentioned about a legend of lizard people that lived in those tubes. She called them either Mu or Mo'o people. I was young and thought that was kind of fanciful, but now I wonder.
I can believe that.