A Storm on the Horizon
The Underdark is a vast series of tunnels, caves and caverns located below the Surface of Akeroth. Its extent is not known, however, it is divided into several sections.
Upperdark: The first three miles of depth that is the Underdark. Most of thise who venture into the Underdark rarely reach any deeper. This area while not as dangerous as other areas of the Underdark is still incredibly dangerous, but its riches are equal (Dwarven cities are technically located in “The Underdark Proper” solely due to depth, however, few Dwarven cities actually connect to the Underdark). Dwarven cities in the Regions of Olfgar and Hildragr reach depths of this level.
Middledark: This area is located three to ten miles beneath the surface, and it is this area that houses the majority of Underdark cities, specifically those of the Drow. The Drow, along with Kobalds, Goblins, and numerous other creatures occupy this area, and surprisingly it is home to the largest population centers in all of the Underdark.
The Dark: Past the ten mile depth marker lies The Dark, here the darkest of creatures dwell, and even natives of the Underdark loathe to venture into The Dark. Contrary to what many would believe The Dark is populated by several sentient Creatures and boasts several enormous cities, but few ever make it to them (and few would want to). Among the depths of the Dark lay the most wicked and corrupt of creatures, and the stories that stem forth from the Dark are ever-telling of the horror and anguish that exist in this dark and deep sub-straight of the earth. Creatures such as Illithiads, and numerous other Abberitions make their homes here (along with the Duargar), but besides them, some, more accepting creatures also inhabit this landscape.