Region: Grace of Gaia
I'd have to go with desert. Both places would try to murder the shizzles out of me (probably both would succeed) but I think the desert has the highest shizzle keeping chance.
Definitely the treehouse. I can tell someone "Wanna see my treehouse?" and there would be a chance that they'd say yes. But if I ask someone "Wanna see my bunker?" there may still be a chance they'd say yes but also that they'd call the police. But of course none of this would happen because I'd never invite someone. This depends on how extensive either option is tho. (Do both have water, electricity, are well isolated from the elements, have other things to make life easier, etc.)
A purple moon would be cool. A cheese-yellow moon too. But I would have to go with blood red cause that would freak people the hell out.