"meet and pour their thundering streams into Acheron"

The river Acheron
Creative Commons AttributionThe river Acheron - Credit: Samuli Lintula/Wikimedia Commons
 Acheron was one of a number of rivers in the Underworld, and known as the river of pain. It is also a real, physical river in northwest Greece. The Greeks believed that rivers from our world could flow down into the land of the dead.