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. In most cultures the term refers to a neutral or dystopic realm of the afterlife, instead of a heavenly one. Sometimes the underworld is identified as "Hell" because Hell is thought to be under the Earth.
(Note: this includes guardian-type creatures, ghosts, and spirits such as demons, veli, and Cerberus)
Buddhism (Naraka) · Chinese mythology (Diyu) · Christianity (Heaven · Hell) · Ancient Egyptian religion (Duat) · Germanic and Norse paganism (Hel · Niflheim) · Greek mythology (Hades · Tartarus) · Hinduism (Naraka) · Islam (Jahannam) · Judaism (Gehennom · Sheol · Abyss) · Shinto (Yomi)