Spirit Realm

A plane between the Material and Celestial planes that holds the spirits of the dead and their various caretakers.

Geography

The plane is largely a featureless void to anyone who is not already dead or a celestial avatar of death. Living mortals can also see the ghostly wisps of the dead, but the spirits don't notice living mortals who enter the Spirit Realm unless the living people had some emotional connection to the ghost. 
To the dead, they see whatever they expect to see in the afterlife in accordance with their beliefs. In addition, if they expect to be reunited with their loved ones, those spirits will actually be connected, but only if those spirits are in the Spirit Realm.
The Spirit Realm is radically different to Psychopomps and deities. These groups see the real Spirit Realm and the spirits in full detail. The true Spirit Realm looks much more like a large forest that you would see in the Material Realm if that forest had somehow been drained of color. The terrain is different in certain areas, but the lack of color is the same throughout. 
There are also many structures, including entire towns and castles, built by the deities and psychopomps. The walls of these structures are invisible to living mortals and dead alike, but spirits can't walk through them. As a result, spirits wander through all the empty spaces of the Spirit Realm, but can be kept out of (or kept in) walled spaces.
Outside of the celestial-made structures, the true Spirit Realm has several notable natural features. The largest of these is the Empty River, which completely bisects the Spirit Realm in a winding path. The Empty River is called this because it appears to be simply a long, deep, empty ditch. However, if you go into the ditch, you will feel yourself being swept away by a fast-moving, invisible force that feels a lot like water Psychopomps can use boats on the Empty River, but only if they are made from materials native to the Spirit Realm. Otherwise, anything put in the Empty River will sink to the bottom and, eventually, be sucked into the soil of the river and vanish.
Another notable natural feature is a large swamp to the southwest called the Swamp of Sadness. Spirits who died with very strong regrets tend to congregate here and it is thought that their feelings influenced the landscape itself, creating a swamp that heightens those feelings of sadness and regret in a kind of feedback loop. This is one of the most dangerous places in the Spirit Realm for those who aren't dead because it will bring out a person's own regrets, drawing them deeper into the swamp and down into the soil itself. At the same time, the spirits in the swamp are always looking for a way back into the material realm so they can complete their unfinished business. This means that a spirit may attack a living creature in the swamp to take over their body.
Finally, the Spirit Realm has a large canyon to the southeast that appears to have no bottom. Appropriately, this has been named the Bottomless Pit. The psychopomps have used this pit as a kind of makeshift prison for undead creatures who can't be destroyed (such as liches with well-hidden phylacteries) because once a person is dropped into the Pit, they fall forever through a neverending darkness. The psycopomps have built a guard station near the Pit to act as guards in case any of the undead in the Pit find a way to escape.

Localized Phenomena

If a living person enters the Spirit Realm, they may be in danger of attracting the souls of people who they have killed or who otherwise hold a grudge against them. If a large number of souls gather in this manner to attack a target, they may create a localized "spirit sink" that starts to pull the living person's soul out of their body. If this happens, the living person's body may be emptied and occupied by a spirit (or potentially multiple spirits).

Maps

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  The Spirit Realm

  A plane midway between the Celestial Plane and the Material Plane that houses the dead.

Alternative Name(s)

Realm of the Dead; Ghostly Plane

Type

Planar Sphere/Grouping