Netherworld

From -("beneath, lower") + world.

Full definition of netherworld

(plural netherworlds)

The place to which one's spirit descends upon death, conceived as below the surface of the earth.In some religions, one's soul departs to a netherworld, hell, instead of the heavens.
The locale of the spirit world or afterlife, whether deemed to be situated below the world of the living or not.While I was astrally projecting, I felt my soul pass through many insubstantial netherworlds.
Specifically, a location of punishment in the afterlife; a hell.The missionary was motivated by a sincere desire to rescue souls from eternal torment in the netherworld.
(by extension) A hidden, shadowy, or sinister subculture, such as that of organized crime.Richard had been initiated to the netherworld of dog racing by his father, and knew all the popular greyhound performance enhancing drugs.

Depending on cultural context, it may be appropriate to construct this as the netherworld, if only one is supposed to exist.

(subterranean region for spirits of the dead) Hades, hell, nether region, underworld
(location of the spirit world or afterlife) astral plane, heaven
(place of punishment after death) damnation, Hades, hell, underworld
(hidden, shadowy, or sinister subculture) underworld