need to live in a fantasy/sci-fi world with a "topside"

yeah I'm just going topside to scavenge for supplies, send a party if i'm not back within two hours.
careful, those are topside rats, they're irradiated.
what do you mean you're going topside, don't you know it's dangerous??
anyone can go topside but nobody ever comes back...
you know i hear that there's a whole other world up topside and the council is trying to keep it secret from us.
selling genuine topside artifacts! still glowing!
nobody's been topside in 30 years. i'm going to be the first. but i really really want somebody else to do it instead so if any of you would like to volunteer
you're from the topside? that's impossible...