Boneyard

The Boneyard is another plane of existence, a limbo of sorts that pulls on all creatures, both dying and dead, enticing them to move to the next stage. The light at the end of the tunnel quoted by those with near death experiences is often one seeing a glimpse of the stark white expanse and dull greys of the Boneyard. When one fails to overcome injuries and stabilize, it's suspected that this urge to join the Boneyard, overtook that being's will, and a new journey has begun.
As the Boneyard is considered a purgatory and "waiting room" for spirits it has become an unspoken neutral ground for all the divine and other interested parties that may seek to gather a soul. It's unclear if this is because of every spirit's natural pull to it, its hostile nature, or if some kind of unmatchable power protects it from outside influence.

The Boneyard

When one dies, their soul is naturally pulled to the Boneyard, another plane of existence made entirely of polished marble, bone, and dust. This plane is only lit by the other souls of the dead, often appearing as blue, white, and yellow wisps as they wander for purpose. While most souls never make it further than the vast expanse of the above ground, an unlucky soul may accidentally wander into one of the many wailing rivers that crack the landscape and flood unknowable ruins. A soul trapped in a wailing river often is stuck, forced to join the countless others that rush past them unless saved by divine means or pure chance as they crash along jutting, massive bones.
If one does not find themselves in a river, it is possible to suffer a fate worse. By entering one of the rare mausoleums that dot the upper landscapes, you'll suddenly find yourself deep in a dark, winding series of hallways often littered with forgotten remains of long-dead things and empty coffins. Unluckier still, if one wanders too far, and too deep into these catacombs (often by accident) they may find themselves face to face with a soul-devouring creature. Often, these beings made of shadow and negative energy will dangle a single white light ahead of them as they stalk the hallways, granting their newest victim a brief sense of hope or at least a chance at companionship before vanishing forever. It's unknown if an encounter with one of these beings has ever been survived, and as such, they yet not have been named or depicted in stories and art.
If one arrives in the Boneyard however, they are not doomed to wander endlessly, and may instead be visited by a psychopomp, a shepherd of souls desiring to lead them to another realm. Oftentimes, these soul couriers represent a specific realm or being, such as the psychopomp of Skrill, a massive moth that seeks to drag her faithful's souls to an ethereal realm of dreams and endless imagination or The All Mother's antlered bear, seeking warriors and hunters to bring to her endless grove. Others, particularly those that made dark dealings in life, may find themselves being summoned and bonded to ghostly imps, who seek to drag them to their demon lords and masters.
If one is quick enough with resurrection magic, however, it is possible to snag a soul before they are dragged elsewhere. Relying on either the dark energies of necromancy or the blessing of a divine, these souls can find themselves in many different forms upon returning to life. One raised by arcane magic may be trapped within a zombie or skeleton, mindless and simply waiting in a timeless state until once again their souls are freed. One risen by divine magic may find themselves simply in their previous body again, but if a cleric is simply not strong enough to do so, may require they be forced into another, constructed body, possibly even as a different race from before.

Citizens

The natives of the Boneyard are few and rare and are typically undead in nature. Skeletons held together by negative energy, flying ships made of bone, and even rumors of a banished lich roam the surface. All of these beings however have a primal, unexplainable fear of the catacombs and the mausoleums and avoid them entirely.
The most common conscious entity wandering the wastes however are Graveknights or oathbreakers, beings granted powers by gods or others that have since betrayed their duties, and now remain unclaimed by their gods. Often driven mad by the nothingness around them, these once-powerful beings have spirits too strong for mindless wandering, but not strong enough to will themselves back into other planes of existence. Due to the length of time these Graveknights spend in the Boneyard, there is a legend of a massive fortress constructed of the only materials found on the plane, bones and ash.
Considering the massive bones of long dead creatures, it's suspected some kind of superfauna existed once naturally in the boneyard as full time residents, and possibly as protectors. These large, dragon and serpent corpses however have been drained of any flesh and marrow by Boneneedles, 8-legged and spindly white ooze creatures that form dens in the few caves and shelters around the Boneyard.

Flora

While an estimated 200 total plants live across the whole of the Boneyard, they are known for their extreme potency and cost. These plants, due to the plane they grow in, are often sought for darker magic such as necromancy and harming spells. The most well known plant among the 20 or so species found in the boneyard is the Black Lotus, a rare flower that only grows in solitary places, with the common myth being that they can only grow in places no spirit, undead or living thing has ever seen. If a creature were to consume a black lotus, it is said one would become a god, and as such, is said by many to not even exist.
Otherwise notable, a red thorny bush grows in large patches (typically a single bush that can grow up to 3 miles in diameter) that when it pricks the skin, is said to steal a part of its owner's very identity and cause a scarlet scar that even the divine cannot mend. This plant, dubbed the "Soul Leech Bramble" can very rarely grow in graveyards filled with restless dead. It's been theorized that these brambles are the Boneyard attempting to drag those restless souls back to it's native realm.

Type

Dimensional plane