With enough distance, the entirety of the Inner Sphere appears metaphysically like a sun, as it is clad on the outside by the Plane of Fire. Beyond this burning surface stretches a void known as the Astral Plane that continues for an unimaginable distance until one reaches the edge of the Outer Spheres. Like an actual star, the Plane of Fire churns the metaphysical substance of the Astral into clouds and eddies that sometimes coalesce into demiplanes.1
The River of Souls
The only true constants within the Astral Plane are the countless branches of the River of Souls: the never-ending stream of souls making their way from the Material Plane to their final destination in the Outer Sphere. Carried along by a silvery haze, most inhabitants of the Astral Plane give the River a wide berth, or else seem incapable of perceiving it; it is unknown whether this is because of a law of the Multiverse or by deific fiat. The River of Souls is monitored (either because of self-interest or benevolence) by countless servants of the gods, who help protect the souls from predators, and help to ensure that they finally reach the Boneyard.1
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