Located by Mars rovers throughout earlier visits has been Basalt a common material found in Martian bedrock. Basalt is something that is common not just on Mars, but the Moon, Io (the 3rd moon of Jupiter) and the asteroid Vesta. Oh yeah, and Earth. If you are asking yourself how is that possible consider this; basalt rock is formed from the rapid cooling of basaltic lava. Source rocks for the Balsaltic Lava are thought to be peridotite and pyroxenite. The tectonic plates here on Earth deep in the ocean are composed predominantly of Basalt, and are produced from the constant incursion of new plates from the mantle below.
The idea is to utilize this basalt as it not only has good insulating properties, but would provide protection from radiation. Also it would solve the problem and cost of carrying several Mega-Tons of building supplies to Mars. In order to do this, robots would seek out large quantities on Mars of these buried columns of Basalt. (Remember – this is formed from lava so it will appear in columns.) Once located and tested for strength, the robots would dig down, opening up a cavern of sorts by removing the weakest columns.
The next step is saved for when the colonists or rather humans arrive. Figuring out which caverns will be used for what purpose from industrial to agricultural, residential and public areas, they would then install the necessary life support systems, power plants, doors & windows.
There is lots that can be done with this design to possibly make it more conducive to whatever work they will be doing, but it is the best design thus far as it would certainly be better for the psychological well-being of the colonist. The previously (offered by most) pods are great for a weekend camping trip but will get old extremely fast.
Interesting to note; apparently the Martian soil is excellent for growing asparagus. Two thoughts: one-it is one of my favorite vegetables but it seems not everyone feels that way, but two-excuse me, isn’t this for colonists who have already traveled all the way to Mars possibly to never see the Earth again. I think they would be happy to eat the vegetable even if it wasn’t one of their favorites previously.
It would be somewhat amusing if our robots set up this colony and then before the colonists from Earth could get there, someone else did!