The Deep Dark

The Deep Dark (or the Underworld) is a massive cave system that runs all over the world and goes as deep as the Heart of the World. The countries in the Overworld sometimes have a massive passage that will lead into the Deep Dark. When a person commits a terrible crime, they will often be forced into the Underworld instead of being executed. The only way out of the Underworld is to go through the Gatekeeper and his Challenges - which haven't been beaten in hundreds of years (not since Tyrag).

The Deep Dark was created by the ancient and supposedly extinct Kul-turu race, but it is now inhabited by criminal humans who have attempted to form an empire called the United Imperium (U.I).

Geography
The Deep Dark is split into multiple regions and areas. There are two primary regions - the Inner Regions and the Outer Regions. The inner are the primary areas of the Underworld, and are walled off from the rest of the cave system with only two known entrances/exits (they are also the most densely populated). The outer is any area that is not inside of the Inner Region, and it is much more massive and unexplored.

There are also places that aren't classified as Inner Region or Outer Region, such as the Living World or the Fathomless Abyss.

History
The Deep Dark was originally a very populated and rich place, with the entirety of the Kul-turu race living inside of it. The history of the Underworld went downhill after the Kul-turu race went extinct after the Awakening of Durycus, in which the Ultimate One ended their lives and thus their empire.

After that, the Deep Dark became a lawless and very dark place after human countries began to dispose of their criminals by using it as a sort of "punishment". The lawlessness ended after Alberis arrived to the Underworld. He founded the United Imperium and took over the Inner and Outer regions and united them into an empire. His greatest achievement however was the creation of The Light, which is a very bright blue glow that emits off of the roof of the cave walls and acts as a sort of sky. The happiness ended when Alberis was driven mad by the mental powers of Durycus, and he went into exile and created the Dweller race - which led to the Dweller War.