The Underdark

There is an entire ecosystem below the surface of Kyor that has yet to be explored. There are several known entrances:

The Underdark Gazeteer

The Underdark is an expansive series of caves and tunnels that reach far into the darkest, deepest reaches beneath Kyor. Surface dwellers can only dream of the horrors that might live deep beneath the ground, and rumors of what lurks below swell within settlements across Kyor. The region is largely comprised of tunnels that all interconnect and often find their end in massive, sprawling caverns. Many of these tunnels are burrowed from enormous beasts such as great purple worms, while others are mined and hewn by civilizations of Drow, Duergar, and other dark races that have rarely, if ever, seen the light of day.

Here is a list of important places in the Underdark in no particular order.