Karkharos

Karkharos is the underworld, the nether-world, the abyss, the pit; the lower realm in the tripartite ordering of creation. Its gateways lie deep beneath the molten bowels of Urva, as far below the mortal realm as the bottom of the ocean is below the vault of heaven. Karkharos is the dwelling-place of the gods of the underworld and all their attendant demons, devils, fiends, and wicked spirits; just as mortal beings have divided Urva into many lands and kingdoms, so the gods of the underworld have divided their realm among themselves into many domains.
The name Karkharos means "Pit of Pits" or "Uttermost Pit" in old Tuvai, derived from "kar" or "kara", meaning simply a pit (the same root is used in the names of the arid basins which dominate Orithea's interior, the Kesh Karkhan, the Kar Kadash, etc.) In the case of Karkharos, a doubling of the basic noun element is used to create a superlative form.