The Underworld

The Underworld is a pale imitation of Creation, similar in geography if not in anything else - although the Underworld doesn't possess the same Elemental Poles as Creation. The land is dreary and grey, and the sun of this realm is a pitiful and pale white.

Shadowlands

Shadowlands can be found all over Creation, excepting the Blessed Isle, where the Elemental Pole of Earth (the Imperial Mountain) closes over any wounds in the fabric of Creation rather quickly. They are areas where the deathly essence of the Underworld has been dredged up into Creation...or where Creation has been dragged down. Either way, they are wounds in the fabric of Creation, where deathly creatures rise with ease and can co-habit with humans.
Some shadowlands are large tracts of land, stretching for unbroken miles, while others are no larger than a cupboard in a basement.
Leaving a shadowland during the day leads to Creation, for living creatures, or the Underworld, for unliving creatures. At night, however, all creatures pass into the Underworld - living creatures versed in magic or bearing a connection to a Word can commit Effort for the scene to pass into Creation instead.
Shadowlands definitively known to the Realm include:

• Marama's Fell - the site of a Shogunate-era concentration camp, located south of Whitewall.

• The Skullstone Archipelago - a string of islands in the northwest, held in thrall by a powerful ghost.

• The Black Chase - a forested region north of Sijan, the City of the Dead, in the Confederation of Rivers.

• Walker's Realm - a shadowland that has been cursed by great darkness, which strikes dead any living being to enter it. Located south of Great Forks.

Ghosts

A ghost is the lingering remnant or soul of a once-living being.

Hungry Ghost

A hungry ghost is the lower soul, the animal instinct, which would normally remain within the corpse and dissipate over time. If buried incorrectly, or not buried at all, the hungry ghost rises from the corpse during the night to attack the living and drain their blood.
Hungry ghosts cannot withstand the light of Creation's sun, and flee back to their bodies before the sun rises. The lower soul of animals is too weak to remain in Creation without assistance from a necromancer.

True Ghosts

A true ghost is the higher soul, the intellect of a being, which would normally enter the state of Lethe, being cleansed of all its memories before entering the cycle of reincarnation. However, if the being had strong regrets or ties to Creation, their soul is instead bound to the Underworld. Many ghosts are incapable, playing out their lives unthinkingly, but a great number are as capable or even moreso since their deaths.
With time, a true ghost can even refine their souls, as mortals and Exalts do, growing in strength over their fellows, as all ghosts are entirely spirit. Since most animals do not possess the same higher soul as humans and other sentient beings, they are unable to leave behind a true ghost.

Nephwrack

Although a nephwrack is a true ghost, scholars and savants group them distinctly from their traditional counterparts, because nephwracks are stark raving insane. At their core, a nephwrack is a ghost who has been corrupted by the promise of Oblivion and is driven to bring true death to everything else as well. Most nephwracks still take humanoid form, although they are capable of reshaping themselves.

Hekatonkheire

The term hekatonkheire is a catch-all used to refer to the ghost of anything that is not and has never been human. When a behemoth is killed by the Wyld Hunt, it may form a hekatonkheire - likewise, when Second- and Third-Circle Demons are truly slain by the Exalted Host, many reform in the Underworld as hekatonkheires.
Most hekatonkheires slumber restlessly below the Underworld, taking up residence in the Labyrinth.

Scholarly Knowledge

Only the most learned scholars of Creation are aware of the following, although a great degree of it is known to the inhabitants of the Underworld.

Oblivion

At the centre of the the Underworld, where the Imperial Mountain (the Elemental Pole of Earth) stands in Creation, there is a deep, cavernous hole, pitted with caverns. This is the Mouth of Oblivion, from which the Labyrinth and the nephwracks originate.
Descending far enough into the Labyrinth brings one to the tombs of the Neverborn - the corpses of the slain Primordials. Descending even further leads to Oblivion, the final end. Anything that enters Oblivion is truly destroyed.

The Labyrinth

The Labyrinth is a maze of tunnels that extend out from the Mouth of Oblivion at the centre of the Underworld and reach to all corners. Space is bent in the labyrinth, making it a very convenient method of travel - however, it is inhabited by necropoli of nephwracks, slumbering hekatonkheires, and worse dangers besides, making it an exceptionally dangerous method of travel.
There are safer places in the Labyrinth, most commonly found closer to the surface of the Underworld, and the use of a 'safe' route through the Labyrinth will often be the lifeblood of an unliving settlement.