A note - I want to explain setting via other things (monster background, relics and artefacts, magic spells, etc) as often as I can. This is for three reasons; It's encouraging for players to find out things about the world by piecing things together rather then being told, it means players and GM's who are uninterested in the setting (usually because they want to make their own) can glaze over it or alter it at their leisure, and it prevents game books from becoming overly padded.
That said, I can indulge myself here and there, right?
Regions of the Known World
The Wistful Dark - A lost land that never sees the sun. The landscape is dotted with the ruins of Old Akenia and strange flora and fungi that feed off ambient mana. Creatures warped completely by shadow wander, driven by a hatred of light. The Tenbrates were born here, and do their best to survive in an unforgiving but hauntingly beautiful realm.
A few here seek the solace of the Star-Shards, pieces of the sun that fell to the surface. These grand crystals create small areas of twilight that drive off the worst of the shadow-creatures and allow civilization as we understand it to thrive. Occasionally, the light of these shards begin to dim and their keepers must seek ways to restore and maintain them.
The Mana Blight - Neighbor to the Wistful Dark, this wasteland is the sad remains of one of the three great empires. Their zealous misuse of sorcerous weaponry left behind a dismal legacy; what creatures survive here are twisted and horrible beyond comprehension.
There is however, a wealth of old world treasure to be found here if one is willing to seek it. Rumors that the old tree of life still manages to grow somewhere in this place has drawn out many eager adventurers to their untimely demise.
The Blazing Garden - On the other end of the world lies a continent where day is eternal and the watchful orb of the Emperor of Sol hangs in the sky vigilantly. The Promethean people make this place their home among the other humunculus species. It is also populated by things large and dangerous, their growth unhindered and in fact supported by a land of plenty.
While Emperor Regulus once ruled this place without question, he is now troubled. While food is in abundance, populations have swelled to the point that land is not. Strife is widespread and large scale war seems inevitable. On top of that, a mysterious child known as "the wicked prince" leads a group of dream-molded creatures on an endless, marauding parade.
The Buried Kingdom - Beneath the surface is an old land, untouched by the constant struggles of the overlord. Those here tunnel tirelessly in hopes of finding glories of the old dwarven kingdoms and the hidden world of Promise. They often find death at the hands of the bizarre horrors and hazards to be found there.
While this place's most consistent promises are madness and oblivion, many confirm that both the old dwarven rumors and Promise are real. Though, so are the strange and horrible caverns warped by the abominations that dwell in them.
The Sea of Shadows and The Glimmering Waves - The ocean of the world is split in two, one where the constant sun reflects off the pristine water and another where unaccounted shadows swirl beneath. There are dangers in both; the sea witches rule the dark half of the ocean while sapient alien reef holds dominion of the other.
Sailors on this contested ocean must be prepared to deal with the dangers of one or the other. The most ambitious must contend with both, as well as braving the twilight merdian; a sort of estuary where the separate oceans clash.
The GM's guide will likely contain an abstracted map of the world, as well as a more detailed area and sample adventure set in the Wistful Dark.