Massive lava tubes on the moon and Mars could be used by astronauts - CNN

Lava tubes beneath the surface of Mars and the moon could be large enough to hold entire cities and skyscrapers, according to a new study. The caves could provide shelter and create exploration opportunities for astronauts in the future. https://www.cnn.com/2020/08/19/world/moon-mars-lava-tubes-scn-trnd/index.html