underworld

n. criminal domain, organized crime; hell, netherworld, Hades; (Religion) of or pertaining tot the world of the dead; world existing beneath (for example beneath the surface of the sea)

In the study of mythology and religion, the underworld is a generic term approximately equivalent to the lay term afterlife, referring to any place to which newly dead souls go.
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Noun
1. the criminal class
(hypernym) class, social class, socio-economic class
(member-meronym) organized crime, gangland, gangdom
2. (religion) the world of the dead; "he didn't want to go to hell when he died"
(synonym) Hel, Hell, Hades, infernal region, netherworld, Scheol
(hypernym) imaginary place, mythical place
(part-meronym) Acheron, River Acheron
(classification) religion, faith, religious belief

(n.)
The portion of the world which is below the horizon; the opposite side of the world; the antipodes.
  

(n.)
The mythological place of departed souls; Hades.
  

(n.)
The lower of inferior world; the world which is under the heavens; the earth.
  

(n.)
The inferior part of mankind.
  

[Other] Among many religions the lowest part of the world, usually represented as the realm of the god or goddess of the dead. It is here that the spirits of the deceased stay. The underworld is seperated from the world of the living by an impassable abyss or river (such as the Styx). The entrance to this realm is often guarded by a huge monster, such as the Greek Cerberus and the Norse Garm. The Greeks and the Romans had their Hades; the Egyptians Duat; in the ancient Indian mythology eggshaped worldview Brahmanda it was called Naraka; the Germans called it Helheim; the Incas called it Uca Pacha; the Aztec referred to the underworld as Mictlan; and the Maya believed in Mitnal.