The Underworld is one of several magical planes. It is where most demons and other evil beings are born and reside. The Underworld is an endless labyrinth of volcanic underground caverns. Unlike the name suggests, the Underworld is not located under the earth, but exists in a seperate plane. There are few entrances to the Underworld and the most common way to reach it is through teleportation.
The Underworld is commonly ruled by the Source of All Evil and ruled by the Triad in his absence. However, since their vanquishment, the Underworld has been caught in a power struggle between the forces of evil. Upon her resurrection, the Morrigan took control of the Underworld, causing it to become overgrown in moss and plants.