Stygia

Stygia was the fifth layer of the Nine Hells of Baator. A vast frozen sea dominated by ice floes and icebergs, it contained the divine realms of Set and Sekolah. It was named after the River Styx, which crisscrossed its entire extent.

Geography
Stygia was a vast ocean of saltwater that was almost completely frozen. Its surface was almost entirely covered in ice floes and icebergs that crowded and completely covered the ocean. The only open body of water was the Styx, which kept its dark, oily water separated from the saltwater and meandered through the layer as if it were crossing a plain.

Some of the ice floes were large enough to support cities. Navigation between settlements was made relatively easy by the presence of the Styx. Small arctic plants grew in some locations, creating vast icy swamps that were slightly warmer than the rest of the layer. Those areas attracted several creatures and wildlife, but were at a larger risk of the thinner ice breaking.

The sky of Stygia was in a state of perpetual twilight and was constantly struck by lightning, which made it extremely dangerous for flying creatures. Thunder swept the land in a continuous rumble.

Stygia was unique among the layers of Baator in that it was almost entirely untamed and wild, with no significant part of its territory devoted to any particular purpose. For that reason, its wilderness was inhabited by several aggressive creatures such as dire wolves, frost worms, krakens, mammoths, polar bears, sharks, and remorhazes, which were used as practice for devils in military training.

Government
The layer was ruled by the archduke Levistus, who was kept prisoner deep within a large iceberg known as the Tomb of Levistus in Tantlin's harbor. Levistus issued his commands and gathered information telepathically, as he was able to communicate with any other devil within 10 miles (16 kilometers). Levistus also controlled all of the amnizus, while he secretly planned to conquer another layer of Baator.

History
Before Levistus's rule, Stygia was ruled by the archdevil Geryon. After Levistus killed Asmodeus's consort Bensozia, he was imprisoned within the layer's ice for millennia, until Asmodeus ousted Geryon and transferred control of Stygia to Levistus. Asmodeus, however, did not grant Levistus freedom, but instead kept him within the ice and decreed that, as part of his punishment, Levistus must offer escape and safety to desperate individuals. Able to conduct all his affairs from within the ice, Levistus then became expert at trading souls of the prosecuted and criminals in exchange for a quick escape.

Rumors & Legends
Stygia was rumored to have been originally a world in the Prime Material plane that was doomed to destruction. Its inhabitants then pledged their entire world and their souls to Asmodeus in exchange for safety, which resulted in their world becoming one of the Hells. This hypothesis was based on the unusual variety of creatures native to the Material Plane that inhabited the layer, although no more decisive evidence had ever been found to support it. It remained a topic of speculation whether the original world's riches were still buried under the ice.

The layer was also rumored to be the headwaters of the Styx, both due to the river's ubiquitous presence throughout the landscape and to the strength of its memory-draining effects there, which were capable of erasing an individual's soul.

Notable Locations

 * Ankhwugaht, realm of Set. It was inhabited by numerous liches and mummies, who occasionally left the realm to trade with the other layer's inhabitants.
 * Sheyruushk, realm of Sekolah, located below the frozen surface.
 * Tantlin, the City of Ice, largest city of the layer. It was built atop an ice floe on one of the banks of the Styx and was ruled by an unknown pit fiend.

Inhabitants
In addition to the wildlife that inhabited the layer, tribes of frost giants also wandered across the ice with no fear of the devils.

The diabolic population of the layer included abishai, amnizus, erinyes, gelugons, and spinagons. Also uniquely among the layers of Baator, pit fiends were exceedingly uncommon in Stygia. Hamatulas and succubi were also commonly found.