Tartarus / The Abyss

"A terrible form. A world made of flesh, fire, brimstone and poison, giving birth to monstrosities beyond anyone's dreams and keeping them alive should anyone slay them".

Manifestation

It is a seemingly endless place, where the ground is made of brimstone, flesh and bone. The places in the Material Plane where water could be found are replaced with fire in the form of liquid by the existence of the River Phlegethon belonging to Hades.
There is a connecting Pathway to Hades in the middle of Tartarus, a tunnel that goes completely vertically, lined with molten rock.
Egg sacs containing new born demons and Evil immortals are distributed along the body of Tartarus.

Localization

It is both the plane and the body of the primordial entity that was born at the beginning of creation. This entity is aligned to Chaos and Evil. Its body is a ground for the rebirth of monstrosities and immortals of Evil alignment in case of their avatar body being destroyed in combat.
It is, much like the Feywild, reminiscent of the Material Plane, but incredibly twisted and effectively not meant for any kind of normal creature.
The only connection where Mortals could be able to travel there would be through Hades, as the only way to use magic to travel there is by using a demon's heart in the creation of a magic portal, which is extremely volatile.

Type

Metaphysical, Demonic