Under-Oerth

Tavern tales across Oerth's sunlit lands whisper of the Underdark, a lightless, subterranean realm that is home to fabled races and ancient, unspeakable evil. It is a domain of primeval mysteries and unending war, a hidden world of cruel masters and hopeless slaves, filled with monstrous races that were old before humans were born. It is a dank, dismal place of fungus, rot, and slime. It is a land where a few lucky merchants have found a lucrative trade, but where many more have been slain (or worse) for their effrontery. So dire is the reputation of the Underdark and its denizens that mothers caution their children to behave, lest the dark elves steal them away.

A proper account of the Underdark must include the cold machinations of the hateful duergar, the unwholesome cities of the drow elves who pay homage to the bitter Spider Queen, and the unending servitude of the lesser creatures that fall into the clutches of these two races. Unlike the upper world, where civilization and the light of day protect travelers from horrors, the Underdark holds the promise of deadly peril. Illithids and aboleths vie for supremacy in its dark tunnels and sunless seas. They fight one another with armies of slaves, terrible and ancient magic, and mind-shattering psionics for control of the encompassing tunnel systems and the extended caverns, vaults, cavities, gaps, and nodes that make up Under-Oerth. The Underdark is literally an entire world, most of which is inhabited by monstrous and evil creatures that shun the daylight. Hundreds of independent cities, towns, and strongholds are scattered throughout the caves and caverns that make up this realm.