Abysses

Vast, empty voids of awesome scope, Tellene’s abysses are rare features that can form insuperable barriers to travel. An abyss is simply a great open space, sometimes many dozens of miles in depth and nearly bottomless. Some Underdark abysses are scores of miles deep. The difference between an abyss and a vault is difficult to define, but as a general rule, a vast space approachable from its higher reaches is an abyss, while the same space approachable from the floor might be better described as a vault. Abysses tend to be larger and deeper than areas that are considered vaults, but this is not always the case. Like the simplest mountains of the lands above, abysses are often completely impassable to anything without wings. Underdark civilizations near such features sometimes carve out harrowing ledge-paths to circle the tremendous void of the neighboring abyss, or endless stairs to descend its walls.