Cocytus

Cocytus or Kokytos (Ancient Greek: Κωκυτός, literally "lamentation") is the river of wailing in the underworld in Greek mythology. Cocytus flows into the river Acheron, on the other side of which lies Hades, the underworld, the mythological abode of the dead. There are five rivers encircling Hades: the Styx, Phlegethon, Lethe, Acheron and Cocytus.