River Styx

Synopsis
The River Styx is a river that runs through the planes, which facilitates the transportation of deceased souls into the afterlife.

Cosmology
The Styx flows through the Ethereal Plane, where it collects the souls of the deceased. It eventually reaches the Outlands, where it flows through the city of Sigil. From the Outlands, the River Styx flows outward in many directions, where it carries souls to their destinations within the Upper and Lower planes.

Within the Lower Planes, the River Styx connects Avernus - the first layer of the Nine Hells - to the plane of the Abyss. As such, it is a frequent battlefront in the Blood War between devils and demons.