Hiya.
I'm gonna go with "Dungeon World"... one of my best friends had this campaign going for a couple of years waaaay back in late '80s and early '90s. It was for 1e with a smattering of 2e. The premise of the world was that the surface had been devastated somehow; magic nuke-war, astrological impact, something...we never found out exactly. Anyway, all of the surface dwellers had moved underground as best they could. Now, folks with no infravision or ultravision (re: 'darkvision') had it pretty rough...going from high man on the totem pole, to low.
Anyway...it was all underground. The whole campaign. Some classes were re-worked to fit better with a purely underground setting (like druids only being found near spectacular natural elemental nodes or in vast mushroom/fungus forest with their own ecosystem, that kind of thing). A lot of really fun and interesting locations.
And before anyone mentions it... no, this was not the "Dungeon World" supplement/setting that came out for 3e by Fast Forward Entertainment. My buddies Dungeon World was, what, a decade or so earlier? Still, my friend did pick it up simply because there were quite a few ideas that seemed to imply that his house was under surveillance by FFE... some right down to the name and description (re: "The Bone Way"...FFE's was virtually identical to ours, but ours was still better.

).
But...if we are talking "video game, movie or book" setting. I'm going to have to go with...
(1)
Legend of the Seeker (TV Series: semi-typical overall, but for some reason the world just kinda felt "real but fantastical" to me).
(2)
DOOM (Video Game Series: ok, so it's sci-fi/horror... but I just LOVE the whole idea behind DOOM [DOOM 1 and DOOM 2;
not DOOM 3]; I'd love to see this done up proper in a good RPG boxed set [and yes, I'm aware of a homebrew DOOM rpg as well as board game and some other side-DOOM stuff]).
(3)
The Fifth Element (Movie: Sci-fi...but man o' man! Tell me the potential for campaign play in that movie setting isn't off the freakin' charts! Shady underworld stuff from 'below the fog' up to CEO's of major corporations, government's, military space, exploration, ancient aliens, ruins, mystical alien artifacts...the list goes on and on! Pure *awesome* is what that setting would be. Period!)
(4)
Morrowind (Video Game: Daggerfall, Morrowind, even some Oblivion and Skyrim tossed in... solid history and good racial intrigue, clans, country loyalists, dragons, undead, all tied together in a believable, cohesive whole, just...wow! Of course, it would be VERY hard to do in a good RPG campaign boxed set...and it would have to be a box set, with a big cloth-based world map kinda like how the DarkSun box had one [the 'second' one; not the first printing, pre-fall-of-whatshispickle...that god-guy trying to go from mortal'ish to full-on dragon]. Yeah, a nice, well-done boxed campaign set of "Morrowrim"

).
^_^
Paul L. Ming