What river does Odysseus encounter at the entrance of Hades?

The river Odysseus encounters at the entrance to Hades is Acheron. In Book 10 of the Odyssey, Circe directs Odysseus toward the land of the Cimmerians and the meeting place of the rivers Acheron, Pyriphlegethon, and Cocytus.

Odysseus does not enter Hades through a simple underground doorway. He reaches a boundary landscape where the rivers and the sacrificial trench form the setting for his encounter with the dead. There, he performs the ritual Circe prescribed so that the shades can approach and speak.

Acheron became strongly associated with the Greek Underworld and is often called the river of woe. In later mythology, Charon ferries souls across it, although other traditions assign that role to the Styx. The real Acheron is a river in Epirus, northwestern Greece, which helped anchor the myth in a recognizable landscape.

The most common mix-up is Styx. Styx is another Underworld river, famous for its oath-giving power, but Acheron is the river named at Odysseus’ approach to Hades in Homer.