Styx

Styx, in Greek mythology, a river, the entrance to the underworld. It was often described as the boundary river over which the aged ferryman Charon transported the shades of the dead. However, early Greek writers identified the river across which Charon ferried the souls of the dead as the Acheron. The River Styx was personified as a daughter of the Titan Oceanus, and Styx was the guardian of the sacred oaths that bound the gods.

The actual river, the modern name of which is the Mavronéri, is in northeastern Arcadia, Greece. It plunges over a 183-m (600-ft) cliff, then flows through a wild gorge. The ancient Greeks believed that its waters were poisonous, and the river was associated with the underworld from the time of Homer.