If you followed the link you may never think about Excel spreadsheets the same way again.
Putting the 'one million people on Mars' to one side, here are some other options:
- long-duration refuge sites buried deep inside the mountains;
- a (largely) self-sustaining lunar colony;
- asteroid or orbital habitats.
I would much prefer self-maintaining and self-reproducing technologies (aka 'life') which could be engineered to thrive in these hard environments and could create an ecology in which even underskilled and numerically-depleted humans could survive and progress.
Maybe needs a similar reworking of human, though (see this post).