if humans are new, have other races. elves who live in the tangle, a wicked maze of razor sharp crystals only the craftiest and most agile humans can navigate more than a few rods deep before dying.
have a race of centaur folk, wild savages who for the first time in history are gathering into a great horde to strike at the greatest of human cities.
there is a vast desert region that men who worship dark things in small caves and warrens beneath the earth have been exiled to. rumor has it they have learned to tame the ravenous ur-hyenas, to ride them and drink their milk. they have made a bargain with the horse-men to split a small alliance of recently formed city-states that have been founded as modest fortresses on top of steep but low rising plateaus (there are few, if any mountains in this world, or at least near the desert.)
great rivers of magma course through some places, and wondrous works can be constructed by men and elves who know the ken of the lava, able to guide it's coursing to create vase, hollow rock structures, or in the case of elves, expand their crystal forest.
Vast fields of low growing vegetables, rice marshes and above all else, many types of fast growing hardy and flavorful fungi grow rampantly. in some regions slime molds and insects the size of 2 centaurs roam about.
the sky is the ocean. the odd gravity of the place has a null zone in the clouds, full of large, gas bladder filled sky ecology. everything from shrimp to whales floats eternally through the mists. they are hard to see but a few clever humans who have forged perfect glass lenses from the lava have built telescopes and seen them.
the wild men in the desert wish to ride them for war and have enacted several measures to truck with the beasts, or perhaps subdue.