The River Styx, also called the "River of Blood", was a controversial concept proposed by some scholars regarding the structure of the Lower Realms. It also acted as a similarly contested model of the afterlife. According to the model, the river was a vast waterway that wound through the lower planes, connecting the realms of the dead and the damned. Its course was unpredictable, shifting with the tides of the planes it passed through.
These scholars also believed that the Styx additionally served as a passage for those who sought to travel between the lower planes. Fiends and lost spirits drifted along its currents, bound for their fates in distant realms. Some relied on ferrymen who knew its shifting routes, while others trusted in their own strength and knowledge of the waters. No matter where it ran, its waters remained dark and heavy, carrying the remains of lost souls, and those who touched it risked losing their memories, their minds slipping away like silt in the current.
The banks of the Styx were considered desolate, marked by jagged rocks and barren stretches of land. In some places, fortresses and strongholds rose above the water, their inhabitants using the river for war or commerce. Armies clashed on its shores, seeking control of its crossings or the advantage of its shifting paths. Those who built too close often found their structures abandoned, swallowed by the changing flow.