Lumia, the sun, shines in the middle of a sphere, surrounded on its outside by the darkness - the carnivorous, cold and insane void of the Nether. In this hopsitable sphere, permanent weather systems spin around a vertical axis. Floating islands called ostrovs dot the sky, held aloft by the hand of the Divine Light of Lumia.
Magic comes in two forms: Lumeric magic, which can only be practiced by those on a moral path, and Netherian magic, which permanently blights and destroys the area around a spell.
Lumerium rocks become buoyant when exposed to light, and are harnessed to float skyships which ply the winds between the ostrovs.
The Church guides and rules humanity with an iron hand. Valistan Heretics fight the Orthodoxy, spreading principles of rational thought and "enlightenment". The Cult of Nether worms insidiously into hearts and minds, seeking to hasten the end of days - the Eschaton.
And Lumia has begun to fade.