The River Styx(Plane)

Styx is the other incredible planar river, also looping back into the River Oceanus. It starts in the Gate Plane of Delta Ferra, the Stygian Delta, then flows through Acheron, 3 of the 9 layers of Hell, through the Prison Gateway of Carceri, through the heart of Gehenna and it's many layers, around the Deathway of Hades. The Deathway splits the Styx into 9 rivers, 8 of which then spiral through the infinite layers of the Abyss and through Pandemonium, before reuniting with the Styx proper, and everything flows back into the Delta Aurus.

The Styx is home to many fiends, the Ferrymen being one of the most famous, but not much else. This is because the Styx is the main battleground of the Blood War, and while many things are happy to continue the eternal fight, most mortal and mundane creatures are not in such a mood.