Between the lack of air and the constant bombardment of radiation and micrometeorites, humans will need some serious shelter before we can feel at home on the Moon or Mars. While inflating or 3D printing our houses could be one way to pack light for the long trip, the most efficient method might just be to move into the natural shelter that's already there. Now astronomers have systematically analyzed possible lava tubes on the Moon and Mars [newatlas.com], and found they may be just what Red Planet realtors are looking for.
Living underground is the easiest way to escape the harsh conditions of the lunar or Martian surface, and scientists have already found a few candidates. NASA has found hundreds of deep pits in the pock-marked rock of the Moon that could make good hidey-holes from the elements, and there's evidence of sprawling networks of lava tubes below the surface.
Don't they realize this has been proven to be a bad idea [youtube.com]?