From David Warmflash’s Discover argument for putting the first permanent space settlement on the Moon instead of Mars:

“A colony on the moon, on the other hand, would be within easy reach. Like Mars, the moon has caverns and caves that can be sealed for paraterraforming, along with craters that can be enclosed with pressure domes.

One fascinating lunar colony proposal would utilize the Shackleton crater at the moon’s south pole, enclosing a domed city with a 5,000-foot ceiling and a diameter of 25 miles.  A colony in that location would have access to large deposits of water ice and would be situated on the boundary between lunar sunlight and darkness. Its proponents estimate a Shackleton dome colony could support 10,000 settlers after just 15 years of assembly by autonomous robots.

In the event of an Earth-wide disaster, evacuating people to the moon would be far easier than to Mars. Another, even nearer option would be free space colonies. These would be built using materials mined from the moon or from near-Earth asteroids. The colonies could be located in the Earth-moon system at sites that are gravitationally advantageous, known as Lagrangian points. In these regions, a colony’s distance and orientation to both the Earth and the moon, or to the Earth and the sun, would remain constant. Utilizing Earth-moon Lagrangian points, it would be relatively easy to transport lunar materials to the site of the planned colony and build it, and the travel time from Earth would be similar to the travel time to the moon, meaning a few days with current technology.”