Twilit Seas is a D&D 4th edition campaign beginning at first level. The setting is partially inspired by Spelljammer, partially by Edgar Rice Burroughs’ Pellucidar , and partially by the scientific mind of Freeman Dyson .
Picture if you will a sphere of terrestrial matter light-minutes in diameter, with a sun burning in its centre. A world with surface area millions of times that of the Earth. Unfortunately, such a construction is moderately impossible by the standards of modern science. Fortunately, magical universes require no such limitations.
It is a world surrounding not one sun but two, one burning with a searing light, the other casting rays of darkness. Between the two is the Twilight Star, a superjovian mass glowing dimly red, about which over a dozen planetoids orbit, perpendicular to the solar axis. Filling the places between is not black, empty space but rather a glowing, swirling mass of color called the Aurora. The sphere itself is a world without a horizon, filled with thousands of civilizations, cultures, and monsters, all linked by a single endless, fathomless sea that spans ‘round the equator, bathed in the light of the Twilight Star. To the “North”, in the lands dominated by the Black Sun, the earth is frozen solid, and glitters endlessly white. To the “South”, in the domain of the White Sun, the ground is burnt black, covered with blowing soot and ash. It is only ‘twixt the two, in the Twilit Lands, that life may flourish in all the greens and reds and blues of the aurora.
Our heroes will begin in a small, insignificant corner of this nigh-limitless world, and though its every secret could not be explored in a thousand lifetimes, the tale of their battles may one day travel the world’s breadth, and shake it to its very foundations.
The geography and composition of Koth (as the sphere is commonly known by a majority of its inhabitants) can be found in greater detail inside. So, too, can information on the most common races, religions, political organizations, and other aspects of life on Koth. This, however, is only the broadest of overviews, as the habitable area of Koth is sufficiently close to infinite to allow for every imaginable variation of culture and race possible. Players are more than welcome to contribute their own ideas.