"Lunar lava tubes may potentially serve a role as enclosures for human habitats. Tunnels larger than 300 metres (980 ft) in diameter may exist, lying under 40 m

"Lunar lava tubes may potentially serve a role as enclosures for human habitats. Tunnels larger than 300 metres (980 ft) in diameter may exist, lying under 40 metres (130 ft) or more of basalt with a stable temperature of −20 °C (−4 °F). These natural tunnels provide protection from cosmic ray radiation, meteorites, micrometeorites, and ejecta from impacts. They are shielded from the variations in temperature at the lunar surface, which would provide a stable environment for inhabitants." Source: https://en.wikipedia.org/wiki/Lunar_lava_tube https://en.wikipedia.org/wiki/Lunar_lava_tube