>>10305363Mars has plenty of lava tubes and domes, it was once geologically active.
They'd be an ideal spot to establish a colony because you don't need to worry about excavation of anything but your entry (assuming it's not partially collapsed, then you just need to seal up the open end.
Then you just need to reinforce and buttress anything structurally questionable. Then you inflate giant airbags in the cavern space and build your colony in normal air pressure. Set up your barracks, administration buildings, agriculture, cisterns, and all machinery needed to boot strap you into a position where you can begin expanding the colony and exploiting native resources to expand the colony.
Your first wave digs out space for the second wave. The second wave brings along all the things that you couldn't cram into the first wave, they help establish the self sufficiency of the colony, while still expanding it. Your third wave moves into a nearly functional colony, with their stores filled with tertiary equipment, luxury items, and new blood with the goal of growing the economy of the colony itself.
Once your population starts to get to a certain size, split some off to go start a new city.a few miles away connected by tunnels or surface roads.
Keep doing this until you've got a handful of closely connected cities that develop their own cultures and identities.
Save the surface domes for agriculture and recreational parks and nature preserves.
Knock some skylights into your underground cities if you want. Mars' day is close enough to earth's that it would be trivial to adapt to a martian day for the purposes of natural sleep/wake cycles.
