CS' Rage of Demons
Tavern tales across Faerûn’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 illithids, 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, drow, phaerimms, 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 riddle the earth beneath Faerûn.
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. Tunnels in the Underdark extend for miles, some ballooning into caverns thousands of feet across, only to shrink to spaces too narrow for a halfling to squeeze through. The largest cavern halls are often representations of the surface in miniature, with hills, valleys, underground rivers, and lakes. Most races native to this realm make use of the walls and ceilings of their caverns, accessing the higher levels via natural or magical flight or levitation, or even wall-crawling mounts such as giant spiders and certain breeds of lizards.
The Underdark is divided into three levels. The upper Underdark (Upperdark) is close to the surface, and its residents have considerable interaction with surface races. The inhabitants of the middle Underdark (Middledark) tend to see surface races as potential slaves. The lower Underdark (Lowerdark) is an incredibly strange place filled with alien societies and bizarre cultures hostile to those unlike them.