Answer: universal myth of the descent of the hero (ego) to the underworld (unconscious) to search something. In Greek mythology who descends is: Heracles, Orpheus, Odysseus, Menelaos and many other. They do not always return. The same myth appears in other mythologies. In Mezopotamian myth it is for example the goddess Innana. Christ himself descended into the underworld only to be resurrected. Descend into the underworld makes part of mystery religions (Eleusine mysteries).
Explanation: it is an image, a metaphor of re-birth, re-newal. So-called "katabasis". The same image appears in dreams and fantasies as well. This motive is very often used in art works.
