The River: Styx Picture

How do the children of Hades visit their mother in the summer? They must travel up the river Styx in the dead of night. But the river of death only ever flows in one direction and is treacherous to those who choose to go against nature and rejoin the physical world above.
Styx
Acheron
The River: Styx
The Tree of Unhappy Endings
Shikieiki Yamaxanadu