Greyhawk

   Several years later I would come to play in the world of Oerth. Although most of the action takes place in the region known as the Flaness, and around the Free City of Greyhawk. It was the second setting of D&D, loosed based upon various adventures up until a fully fledged campaign setting was crafted for it in the1E. In later years when western Oerth would be fleshed out in 3E Chainmail miniatures game, where it took place in the Empire of Ravilla.

   Oerth is unique as it is on of the few world that is the center of it's system. Its two moons, Kule and Raenie, while the Sun "Liga" orbits around Oerth. The other planets past Liga are; Edill, Gnibile, Conantha, Ginsel, Borka, Greela, and Spectere. Supposedly Oerth, is one of many parallel worlds that includes Aerth (Dangerous Journeys), Earth,  Nerath (4E Core World), Uerth (Opposite Alignments), and Yarth (Sagard the Barbarian).

   Oerth is also an iconic place. Not only are all the standard race are here, but many many of the named spell found throughout the multiverse seemed to have originate from here. Name's like Otto, Drawmij, Bigby, Tenser, Rary, Mordenkainen, etc... are know across many planes. It is debated though that some of the spells they discovered are actually found in other worlds by other names as well. 

Also unique is many of the standard racces identify themsleves with their Flan pronunciation; Elves of olves, Halflings are Hobniz, Gnomes are Noniz, and Dwarves are Dwur.