The Imperial Cult teaches that the souls of the dead join to something greater: the Strength of the Southern Wind, losing their individual identities but gaining a greater purpose.
Other scholars and theologians often describe the afterlife, either literally or metaphorically, as a place. The southerners call it Cthonus. The dwarven clans and their halfling cousins call it Tarthrunas. The elves have a name for it that they refuse to even speak.
Whatever it may be called, another world exists—under, within, against, echoing—Materia. Secret entrances in treacherous places can convey the living to this place. Such entrances are how the heroes of the legends have ventured into the afterlife to retrieve loved ones or seek the counsel of the dead. They are also how the dwarves and halflings arrived to make their home in Materia… and how the armies of Hell invaded, twice, in the Mythic Age.
The few travelers who have descended to the Underworld and returned describe it as an arid, unwelcoming place, dominated by a vivid red sky and strange foliage. Resources of any sort are scarce and the terrain is rugged. Even so, the entire plane, from the violet grasses to the roiling storms to the crimson skies, possesses a forbidding beauty.
The souls of the dead are said to be called here, and legends relate the living’s encounters with ancient souls in great cities on the wide valleys.
The Underworld lies between Hell and Materia, making it all the more dangerous for the demons that roam in search of ways up from Hell to the realms of the living.
The party has discovered that beasts and monsters, too, seem to be called to the Underworld in death. This can create odd sights, as predators feel no hunger, and as a result, no drive to hunt prey. The wolves they encountered in Sanctuary were by no means tail-wagging, domesticated puppies, but they greeted the party with canine curiosity rather than carnivorous aggression.
The souls the party has encountered in the Underworld seem to manifest physical appearances according to some sort of self-image or reflection of the soul. Guan Jinping appears not as the smoking armored husk that he was when he died in Materia, but as an enormously tall, bearded general: perhaps as he was in his prime, although it is hard to believe any man being so tall. The Steward of Sanctuary has ascribed her ghastly appearance to her deep, abiding understanding—and embrace—of death when she was alive.
According to Algot the Shield, the birthplace of the dwarves, Durad-Om, is in the Underworld.
Hialathar has shed further light on the Underworld’s role as a fortification. The Underworld, he claims, surrounds Materia, encircling it, like a great outer wall, a bulwark against Hell. It has been like this ever since the very first demonic invasion of Materia, eons before history.
Ashkahala, First of the Dead, commands the souls of the dead. They are her levy in the eternal war against the Lords of Hell, constituting the garrisons in the Underworld’s strongholds and the main strength of her armies in the field.