Path of the Wanderer
The Great Sun
The Great Sun is a blistering hot globe estimated to be 100 miles in diameter which rests precisely in the midst of the World. It illuminates on a regular cycle, shining with a massive, near blinding brilliance for 10 hours, dimming gradually over an hour to approximately one percent of the daytime brightness (still too bright to comfortably look at), remaining at that low point for 10 more hours, and then brightening again over an hour to the full rich light of day. During the night time, when the Great Sun is still quite bright but of course much softer, it is dim enough to be occluded when clouds get in the way, and a cloudy night is quite dark.
Stories exist that in the 10th and perhaps the 5th Age, people explored the surface of the Great Sun, and reported finding hostile creatures, curious pits, and an entire abandoned city built of some unknown metal, in which ghostly shapes writhed in seeming torment. No long term exploration seems possible; even at night the Great Sun is perilously hot, and during the day, there's no force strong enough to endure the heat. Even the great fire dragons avoid drawing too close to the Great Sun, day or night, for fear of damage.
There is a vague legend that in an age very long ago, possibly the 3rd, someone (an Icon, it is to be assumed) managed to shift the sun's period, such that it was night for much longer; this had disastrous consequences to farming and much else, and led directly, so some believe, to the chaos of the 4th Age, when Tierzit was abandoned. That worldlet has never been fully resettled by civilization. If its true that the Great Sun was tampered with in this fashion, it has apparently restored itself, or been restored, and no one has managed the feat since.