I was inspired by Dune, where the characters can't really go outside during the day (at least for long) because it's so hot, so they stay inside these massive buildings.
On a planet which is very hot (at the edge of human habitability, around 108 degrees F, maybe even slightly higher on most of the surface), could humans survive by taking shelter from the direct sunlight in the caldera of an exctinct volcano?
I'm thinking of a large volcano like Olympus Mons (its. caldera is 3km deep on overage). Would the temperature be reduced enough for people to survive?
Other issues would be access to water, but perhaps there could be a lake within the caldera or simply enough rainfall to prevent drought.