Eberron: Shadows of the Last War
The Mortal World of Eberron is made up of six continents surrounded by oceans above a vast underworld.
Southeast is the small continent of Aerenal, ruled by elves. Due south is the jungle continent of Xen’drik, once ruled by an empire of giants that collapsed, now largely wilderness, with some areas under tribal dominion of the drow (with a polar continent to the south called Everice). The other two main continents are Sarlona (a continent that few know anything about) and Argonnessen (a continent inhabited by dragons). The world of Eberron has twelve moons; some sages believe there is a thirteenth moon that has vanished or is invisible to the naked eye.
“Eberon” is also refered to as the Dragon Between, Siberys, the Dragon Above, is the name given to the planetary rings which surround the planet. Khyber, the Dragon Below, is the name given to the underworld (and is similar to the Underdark in other settings such as the Forgotten Realms). According to the creation story, the world was formed when the progenitor wyrms changed their form into what they are now. Siberys created the dragons, Eberron created humanoids and other “lower races”, and khyber created the “demons” of the world (The term ‘demons’ is meant to use the common definition, not the D&D outsider).