Pellucidar books were mind blowing for me because of this setting. There was a scene in (the 2nd book) where the protagonist was being chased in a canoe by a bunch of canoes on wide open sea water. He did have to look up to find them. Blew my mind.
Another thing to consider is that spell durations would be effective because it is High Noon ALL THE TIME in the hollow world.
But one particularly interesting thing is Golarion is hollow! See here:
http://pellucidarskartaris.blogspot.com/search/label/Pathfinder
quote:
"Incredible rumors suggest that the beasts that make the realm famous somehow emerged from an impossible underworld with its own false sun, a savage microcosm in which the dinosaurs never died and humans never emerged from their primitive origins. The Pathfinder Society has mounted five expeditions to this rumored inner world, but none of (sic) have ever returned from the country alive."
and
quote:
"Some are said to be so huge that they are themselves inverted worlds, that the denizens walk and live along the inner surface of the vault in defiance of gravity, and that their skies are lit by a glowing orb of brilliance akin to the sun itself floating at the immense cavern's center."