Path of the Wanderer
The World is a hollow sphere of some dark blue, hard material; in places it is marked with lighter matter, snow perhaps, but no one is certain. It's a long way out to the sphere, and there's nothing there if old stories are to be believed, so no one goes that far.
Inside is a vast open space illuminated by three suns: the great burning ball that hovers in the center of the sphere is the greatest of them. It is called, simply, The Great Sun, and it shines brightly for ten hours of the day before dimming to a soft glow for ten more hours. The dimming takes place over an hour, as does the brightening, and thus a full day is 24 hours. There are two more smaller, less brilliant suns. One is called the Errant, and drifts about seemingly at random; it produces light but very little heat, and at times it comes very close to some of the worldlets (see below) or passes within the aura of the sun. Stories tell that it was created in the sixth or seventh age, though no one is quite sure which, and that it was meant to drift about the outer edges of the world and help shed light and heat on those neglected areas, but that something went wrong in its creation or more likely shortly thereafter. Lastly is Unaga, the Sun Goddess, whose body is a hot, bright globe that moves about as her followers call to her. What this means in practice is that often she finds herself suspended between two or more worlds that are each praying for her arrival, and that she does little, bound too closely to the whims of her followers. Some say that Unaga is actually the Great Sun, and that the Hesitant Sun is her child, a simple creature who tries to help but is unable. Irregularly, some city or great temple will exert great and strong prayerfulness, and Unaga the Hesistant will move with alacrity into a new orbit, for a time, until She is drawn away by the collective prayers of hte other worldlets.
There are many objects drifting in their regular paths about the inside of Amur the World, from the corpses of unfortunates to the graceful dragons and pegasi, on up to floating fortresses spun out of the whims of wizards or Icons, and finally the great Thirteen (sometimes called the Moons, the Spheres, the Homelands or the Worldlets.) These massive objects, each hundreds of miles around, move in regular paths through some portion of World, each of them drifting closer and further from the Great Sun as has been dictated by fate and history, sometimes drawing close to their neighbors. A couple of them have elaborate paths which take them though several other neighboring Moon zones; one, the Wanderer, passes in turn through each zone, with such regularity that seasons are named for the worlds which the Wanderer passes by. Passed by, in truth; some of the Homelands no longer occupy the spaces they once did, but the names and seasons remain the same.
These seasons are twelve, each comprised of ninety days and each named for the Worldlet which Wanderer drew closest to in that period. Four seasons comprise a year, which is the span it takes the majority of the Moons to return to the same point on their orbit; three years (all twelve seasons) comprise a Cycle, the time it takes the Wanderer to return to it's starting point, and the other two more vagrant worldlets as well—they process more slowly than the Wanderer, and do not cover as much territory. Note that they encounter the Wanderer in the same place on that Moons orbit each time around, though they move about quite a bit themselves.