Hell

The Underplane, more commonly known as Hell, is the last of the three Prime Planes of Creation. It is a place composed of the fires from the act of Creation, and is dense with energy. Time and space are said to be happening all at once in the Underplane, though the ramifications of this are hard to articulate to life from other planes. There are planets that are referred to as Spheres, but unlike the Midplane where a being must be either powerful enough to teleport the great distances between them or have access to advanced spaceships or other technology, movement between the Sphere is Hell is a relatively simple matter because of the condensed nature of that plane. All locations within Hell are tied together through an elaborate network of portals that the denizens of Hell have managed to learn, though more powerful devils are able to simply teleport between Spheres under their own power. Whereas the Midplane is largely filled with a black expanse, the background of Hell has the appearance of an inferno. No matter what sphere one is on within the plane, the sky constantly seems as if it's burning.
When spirits become heavy with sin, they fall to the Underplane till their sin is burned away and they are light enough to ascend to the Midplane and rejoin the Wheel. The act of torturing these fallen souls is done by the demons who have little sense of what the spirits actually are, finding their sin to be a food source. When Lucifer fell and became Satan, he plummeted all the way to Hell where he crafted a material body for himself, becoming the first Devil. From him came the rest of the race of Devils, and from them the various demon races which have spread throughout the Underplane. Satan constructed the Sphere of Pandemonium as a capital from which he could rule, but following his defeat and imprisonment at the hands of Bahamut, Pandemonium was abandoned and the more powerful devils carved out their own Kingdoms.
==Spheres of Hell==
Floating in the sea of fire are the 666 spheres of Hell, planets of widely varying disposition but almost without exception are swarming with demonic life. Pandemonium sits at the center of Hell with the other Spheres orbiting around it. Unlike the Midplane where the 9 Worlds are consistent, the 666 Spheres are in a constant state of flux, with some growing in powers while lesser Spheres orbit them. Some spheres are the centers of power for the fearsome Archdevils, Devils of incredible power.
===Pandemonium===
A hellish reflection of Crown in the Midplane, Pandemonium is the ancient capital of Hell. It is a bleak, windswept sphere where Satan created a gigantic hall where he could hold court with his devils and their demons. After Satan was imprisoned by Bahamut, Pandemonium was abandoned as the more powerful Devils declared themselves Archdevils and carved out their own kingdoms. Pandemonium fell into disrepair, and was unseen until Satan's revival. He retreated there after his loss of the Bloodstone, and was ultimately killed there by the Magnificent 7.
===Carnia===
Carnia is the realm of the succubae and their ruler Sin.  It is a place designed to overwhelm the senses of those who go there, leaving them as prey to be easily drained of their life essences by the Succubae.
===Moab===
Controlled by Moloch, Moab is a bleak world of grey stone.
===Sheol===
Sheol is the domain of the fearsome Archdevil, Abaddon.
===Malebolge===
The Malebolge is the sphere controlled by Mephistopheles, who rules from a terrible palace in the center of an elaborate network of ditches.
===Houyhnhnm===
Home of the Horse Head Devil, Jabberwocky.
===Inferno===
Also known as the Burning Kingdom, Inferno is a sphere deep in Hell that is the source of the mystical Hellfire. This power was harnassed by the Old One, Amon, who built a thriving empire there. After a cowardly attack from the Devil Abaddon, Amon was mortally injured and sough a successor. He found three Devil brothers who, like him, were sons of Satan, and decided to train them. Only one survived his training, and this Devil inherited mastery of the Hellfire and the throne of Inferno from him. Called Sara, he sired a new generation of Devils with Amon's daughter Naome, and this clan came to be called the Sarans. The Sarans ruled Inferno in a golden age, constantly warring with their neighbors like Moloch's Oni and the "Beast of Hell" Abaddon. At one point a bleed to the Midplane occurred between the Inferno and Ancient Kazan, through which Sara lead his clan. He conquered Kazan, and his Devils bred with the life that had evolved there as a result of being touched by Hell's energies. This mortal race of demon spawn became the scourges of the Known Universe known as the sarans, and were left behind by their Devil forefathers. The Saran Clan returned to Inferno, but during a massive battle known as the Twilight of the Sarans, they vanished from Hell forever. Their Hall was left behind, and since then no other Devil has expressed interest in taking over the Sarans old territory. According to Virgil, since the ascension of the Sarans, the place has been permeated with an energy that other Devils find repellant.
===Cocytus===
Known as the "very bottom of Hell", Cocytus was where the final showdown between Bahamut and Satan occurred, where he has been imprisoned for most of time. He remained frozen there for untold eons. Eventually he was found by the fallen Goddess Lilith, who was wandering Hell after being locked there by her former lover, Adam. After escaping from the Archdevil Mephistopheles, she stumbled upon Cocytus and the frozen form of Satan. She fell in love with him, and decided to free him from his prison and together they would reap their vengeance on Creation. She managed to enthrall Abaddon, by now the most powerful Archdevil, and with him cow other more powerful Archdevils, making herself the effective Queen of Hell. She created a massive palace in Cocytus, declaring it the new capital of Hell. When Satan was released, he destroyed the Kingdom in order to "stretch his muscles."