Abyss
The Abyss is a plane of existence, the alignment of the plane is Chaotic Evil, and this is shown both in the plane itself, and its denizens, the Demon and the Daemons. The difference between the two is small and unclear to the uninitiated, but Demons are created and serve a Demon lord, while Daemons are the creatures that naturally exist in the Abyss, but there are no records of the abyss before the demon lords, so the true nature of the two groups, and their histories, will remain a mystery. The deeper into the layers one goes, the more powerful and deadly the denizens are, and the further away from the material plane they are, making it harder for them to effect it as others do. This has lead many scholars to think what horrors may lurk in the deepest depths of the Abyss.
Geography
The Abyss is a stack of infinite layers, which are the Layers of the Abyss, each of these layers is very different but they have some things in common. Each of them is ruled by a Demon Lord, and all demons in the layer bow to them. Each layers has somewhere in it a portal that leads to the layer above it, and one that leads to the layer bellow it. The portals don't need to be actual portals, and might be pools, mirrors or even a staircase, their origin and locations are unknown. The layers also come in contact with the river Styx, out of which come the souls of mortals damned to the layers, or who have given themselves to a demon lord. If a demon follows the river on its side, it will lead them directly to the first of the Nine Hells, which is how the Blood War is perpetuated, as legions of demons charge towards new ground to conquer, in the name of their demon lords.
