Lava Tubes: Human Habitats on the Moon and Mars?
Source: AlphaGalileo Posted: 10/3/17 Lava tubes, underground caves created by volcanic activity, could provide protected habitats large enough to house streets on Mars or even towns on the Moon.
'There comes a time when the mind takes a higher plane of knowledge but can never prove how it got there. All great discoveries have involved such a leap. The important thing is not to stop questioning.'