How can you get into the Underworld?

In Greek mythology, the guarenteed way to get into Underworld is to die, providing the brurial rites are respected. However, various figures have entered the underworld alive. The locations of the entrance are various and always uncertain. Charon, the ferryman, who ferries the souls of the dead to the underworld, crosses the river Archeron which can be located near the village of Glyki. The souls of the dead wait at the gates of Underworld with coins either over their eyes or beneath their tongue (a traditional burial rite in ancient Greece). The coins are to pay Charon for the service. Only the dead are permitted to cross, so Psyche used this method to get into Underworld. To get passed Cerberus (Hades' three-headed guard dog), she was instructed to feed him a kind of cake.

Orpheus instead charmed Charon to take him to Hades' palace with the music he played on his lyre and by singing. This also calmed Cerburus who let him pass. Heracles found an extrance near Sparta and threated Charon. He then fought and over-powered Cerberus.

Odysseus, at the advice of Circe, travels by ship into Underworld. He sails to the end of the world then makes a sacrifice of a goat, feeding the blood to a prophet who instructs him from there.