The Underworld (also known as the Netherworld or Realm of the Dead) is a place where the souls of the deceased go in many different cultures' mythology. Sometimes it is identified with Hell. Other traditions claim that the Underworld is where all life have originated and where all life must return when they pass away. In most mythologies, some variant of the Underworld does exist, whether it be hell, heaven or the higher planes.
This includes material from Mythology Wiki.