The Deeps

The Deeps are a mysterious network of caves and caverns that lie under much of the Firmwold.

Geography

The Deeps are poorly mapped, and defy mapping by shifting occasionally.
Connections between the Deeps and the surface world are few and far between, but widespread across the Firmwold. Traveling from one surface location to another via the Deeps, if one is able to navigate them efficiently, takes far less time than the same travel across the surface would cost. Scholars debate whether this discrepancy is due to magic, or due to the Deeps having numerous connections to other planes of existence.
Scholars favoring the latter theory are in fact correct. Traveling far through the Deeps includes numerous jaunts into planar spaces that lie between Ferkathas and the Plane of Earth ... and possibly even into planar spaces that border the Far Realm.
Certainly the Far Realm seems to have a special influence over the Deeps, judging by the number of aberrant creatures found there. Indeed, illithids are the dominant political power in the Deeps, if any can be said to exist at all.

Fauna & Flora

Flora that doesn't depend on sunlight, including wild khanegu, grows abundantly in the Deeps, and whatever fauna can subsist off of that ecology. In addition, pockets of magical energy have been found, in which fungi that would normally depend on light feed off of magic energy instead.

Alternative Name(s)

Underdark

Type

Cave System

Location under

Ferkathas