Shadowfell

Shadowfell is a realm located underneath the Earth's surface, home to the creatures known as demons. The entrances to Shadowfell are usually located along ley lines and in other intensely magical places.

The most immediate impression of a visitor to Shadowfell is the lack of color and light; no sun, no moon, or stars adorn the void above, and most things within the realm appear on the spectrum of black and white.

Light sources only illuminate half of the distance that they would on the Surface, and flames and fire put out significantly more heat. Seeker abilities dealing with light and fire are less predictable and reliable in Shadowfell, and are prone to failure, whereas shadow abilities are enhanced. Where light sources do not illuminate as much, they are far more visible in Shadowfell, and can be spotted from up to ten times the distance on the Surface.

Gravity and time are more or less identical to that on the Surface. It is prone to relatively frequent but usually small earthquakes (called shadowquakes).

Early history
Two theories exist as to the creation of Shadowfell; the first is that it was the original Surface of the planet Earth, only to be sent within the planet upon the creation (or evolution) of Humans and Seekers; the second is that upon the arrival of Humans and Seekers, the Ancient Ones (now known as Demons) were banished or retreated to the dark realm below.

Geography
Five rivers run in Shadowfell: River Acheron, River Styx, River Lethe, River Phlegethon, and River Cocytus. There are several ruined slopes and mountains caused by earthquakes. The differing elevations are known as Upperdark, Middledark, and Lowerdark.

Neshiyyah
Neshiyyah is a kingdom also known as Limbo. It is located on the edge of the River Acheron. It is ruled over by Paimon, and is the native kingdom of the Banshees.

Isikat
Isikat is a place where nothing gleams. There are terribly violent wind storms at all times in this kingdom, as well as a ruined slope apparently caused by an earthquake. It is ruled over by Asmodeus, and is the native kingdom of the Incubi and Succubi.

Tit ha-Yaven
Tit ha-Yaven is characterized by a ceaseless, foul, icy rain and the subsequent freezing mire. It is ruled over by Baal.

Gehinnom
Gehinnom is best known for a strange type of jousting that involves great weights, which are pushed with the jousters' chests. It is ruled over by Balaam, and is the native kingdom of the Liches.

Sha'are Mavet
Sha'are Mavet is largely occupied by the swampy, stinking River Styx and the Stygian marsh. The capital city is known as the City of Dis, easily recognizable by the architecture that resembles fiery red mosques. It is ruled over by Beleth, and is the native kingdom of the Gidim.

Tophet
Tophet is notable for the large number of flaming tombs located here. It is ruled by Purson and is the native kingdom of the Faeries.

Mashchit
Mashchit is bordered on all sides by a jumble of rocks that had once been a cliff. There are several ruins located within this kingdom. The River Phlegethon, a river of boiling blood and fire, is located here. The river grows shallower as it reaches a ford, after which it comes full circle back to the deeper part. Also within this kingdom is the Wood of Suicides, inhabited by gnarled, thorny trees that are only permitted to speak when broken and bleeding. Also is the Plain of Burning Sand, scorched by great flakes of flame falling slowly from the sky. There is a great waterfall that plunges into Malebolge. It is ruled by Vine.

Malebolge
Malebolge is a large funnel of stone shaped like an amphitheatre around which run a series of ten deep, narrow concentric ditches or trenches. From the foot of the Great Cliff to the Central Well of Malebolge are large spurs of rock, not unlike umbrella ribs or spokes, which serve as bridges over the ten ditches. There is also a lake of boiling pitch. It is ruled over by Zagan, and is the native kingdom of the Skinwalkers.

Cocytus
Cocytus is comprised almost entirely of a large, frozen lake fed by the River Cocytus. There are several cities within Cocytus; Caina, Antenora, Ptolomea and Judecca. It is ruled by Belial, and is the native kingdom of the Wraiths.