I like it, Muro! and thanks to both of you for commenting. Let me attempt to address a few of Mystic's questions before I forget about them.
Is the convex world only full of happiness and bright sunshine, rainbows and unicorns? Or is it more like the mundane world?
- The Convex, as I imagined it briefly, would be a normal medieval fantasy world. There would be a light undertone of magical things beyond mere mortal comprehension. No flashy magic, like fireballs or magic missiles, but more subtle "powers" like divination and unexplained good, or ill, fortune. I'm open to other suggestions as well, but the typical game in this setting would likely start with waking up on the "Other side."
Is the concave world bathed in darkness and full of things which shy away from the light? Is it home to evil, bloodthirsty, light-hating creatures or do its denizens merely view the world differently.
- Not so much "light-hating" as "not used to light." I pictured The Concave as lit by a starry night, and a hint at light beyond the edges of the bowl where there exists dusk-like lumination. Abd many of the beings living there may be considered "Evil" by normal standards. Cannibalism, theft, and doing what you *need* to do to survive would play a big role. Leadership of the very strong, or very cunning, is likely.
Does understanding the mysteries of the concave world grant wizards more power on the convex world because they are familiar with the unseen powers of the cosmos or does being exposed to its mysteries drive them mad?
- I think both of these suggested outcomes are likely. Where The Concave is a bowl holding in all the foul and corrupt world energies, where things like negative emotions fester, The Convex deflects them and projects them away from the people of that side of the world.
Some more ideas to go with the setting:
The Fogs of Rigor - A thick black mist covers the cracking ground, oozing up from depths unseen. It doesn't even come up past your ankle, but it chills your foot in such a way that it makes you feel unclean. You wish you could wash it, but there doesn't seem to be any water around. And especially no *clean* water. Upon lifting your foot to examine its condition, the feeling of it was quite disturbing, a shocking thought occurs to you. It feel like a part of you has died... A physical part. Your foot. The yellow-toothed old man cackles from atop a small clump of moss, watching you and enjoying your surprise. "The Fogs of Rigor claim another victim, it seems." He unleashes a crooked grin for a moment, but it is quickly stifled by set-in-stone seriousness. "You'll want to climb up here and start rubbing it a bit, or else it'll never come back. Might even spread. No one's been fool enough to touch the Fogs of Rigor for very long."
Scorch-Born - One way of getting here, The Concave, is through conflagration of your Soul. When The Whispered Blaze touches you in the night, for reasons known only to the Cult of Blackened Churches, you are born again... Down here. The Scorch-Born are a rare event that usually coincides with The Yellow Streak, when the Sun briefly touches our skies. They usually wake screaming, as they peel their own charred flesh out of a pod of breathing magma. The Scorch-Born are easily spotted, due to their fried black and bleeding skin that crunches sickeningly where they bent. They are otherwise just like you, newcomers, fresh meat, though well-done.