Hell

The Nine Hells of Baator, sometimes shortened to Hell or Hells, and named Baator (pronounced: /beɪˈɑːtɔːr/ bay-AH-tor) in Infernal, was the home of the devils and the plane that embodied lawful evil. It was a plane of sinister wickedness and institutional cruelty, its denizens organized into a strict caste system with a very rigid chain of command. Each of the nine Hells had its own physical laws or properties of matter, but all were inhospitable or deadly to outsiders. “ From the boiling rivers of fluid in Avernus to the sheer crags of Nessus, a body'd be hard-pressed to find a place that sums up the cold cruelty of the multiverse more than Baator does. ” — Nomoto Sinh, mortal mage.

Each Hell was a different infinite layer interconnected at barriers much like a nine-layered cake—the lowest points of one layer manifested barriers that exited high above the surface of the next lower layer. The river Styx flowed through the first layer, Avernus, and also the fifth layer, Stygia, before crossing over into Gehenna.

Each of the nine Hells was unique and usually mirrored the malevolent characteristics of its ruler, or perhaps the archdevils were shaped by the domains they schemed to control, no one can be certain.
Avernus The first circle of Hell was also the "topmost" because Astral travelers would emerge from color pools on this layer and reaching the next circle required descending to the lower depths to breach a barrier to Dis.
Dis Dis, the Second Hell. The second circle of Hell, when described as its own layer, was a flat barren plane containing little more than black, stagnant rivers, stretching for thousands of miles until it reached some rolling hills. The sky was a cloudy dull green shot through with lightning. In the center of this plane rose the Iron City of Dis, several miles in height and hundreds of miles wide. The foul rivers radiated from a moat big enough to be called a lake surrounding the Iron City.
Minauros Minauros, the Third Hell.
Minauros as a layer was described as an endless bog of vile pollution, decaying bodies, and rotting marsh, repeatedly drenched by rain, sleet, and hail storms. The soggy, bone-strewn, disease-ridden swampland made movement very difficult and was only broken occasionally by serpentine ridges of volcanic rock. Nameless creatures even the devils feared inhabited the swamp. Minauros as a realm was depicted as a broad but low-vaulted cavern connected to Dis. An oily water percolated through the roof of the cave and rained down upon swamps, deserts of mud and oozing black soil, pockmarked by bubbling fumaroles and mud geysers.
Minauros was also the name of the city built of black stone by Mammon on the treacherous surface of this place. Only the ceaseless efforts of thousands of minions and slaves prevent the city from sinking and being consumed by the bog. The city of Jangling Hiter, also known as the City of Chains, hung by massive links of chain above the noisome fen and was ruled by kytons.
Phlegethos Phlegethos, the Fourth Hell.
The fourth circle was the Hell that most resembled the stereotype of a fiery world of eternal damnation, filled with active volcanoes, rivers of liquid fire, molten rock, ash hills, smoking pits, unbearable heat, all wracked by tremors and earthquakes.Even the air seemed aflame and thus Phlegethos was considered to be fire-dominantIn the World Axis view, Phlegethos was a cavern several miles below Minauros, where burning lava poured out of fissures in the ceiling.The city of Abriymoch was the seat of power in this realm, built of hardened magma, obsidian, and crystal in the caldera of an extinct volcano which provided visitors some protection from the elemental environment found throughout the rest of the plane.
Stygia Stygia, the Fifth Hell. The complete opposite of Phlegethos, Stygia was either a bottomless ocean covered by an ice sheet up to 3 miles (4.8 kilometers) thick, or a frozen sea salted with huge icebergs[ buried in a cavern several miles below Dis and hundreds of miles away from fiery Phlegethos depending on which cosmological model was in vog The older model also suggested the Styx supported small but hardy plants and mosses which, after millennia of decay of this vegetation, resulted in swampy areas along the banks of the river. A few floating islands were the only non-frozen ground in Stygia, their peaks wreathed in lightning arcing from the coal-black sky. Where lightning struck, a strange phenomenon called "cold fire" erupted: white flames of extreme cold that "burned" for a short time and then disappeared without a trace. The great city of Tantlin was built upon one of these islands, in the curve of the swampy Styx, or perhaps on a giant ice floe. Due to the proximity of the Styx, Tantlin was a cross-planar trading post for those brave enough to attempt navigating the treacherous river.

Malbolge Malbolge, the Sixth Hell.
There is significant disagreement between cosmologies on the nature of the sixth circle of Hell. As a Great Wheel layer, Malbolge was a gargantuan tumble of angular black stone blocks, each block ranging in size from a small city to a large metropolis, that formed a pile hundreds of miles thick. The randomly tilted and ill-fitting blocks were honeycombed with angular passages and caverns causing non-flying travelers to frequently need mountaineering skills and risk avalanches. Stinking clouds of vapor rose up from the depths and lit the sky with the color of blood, causing cosmologists to speculate that the blocks of Malbolge may have rested on an infinite sea of lava. Corroborating reports have been heard of flammable materials left on the ground spontaneously combusting. Most habitations in Malbolge were copper-clad fortresses built from black stone.
The World Tree view of this layer was similar to the Great Wheel plane of Gehenna: a steep, infinite craggy incline often subject to avalanches that crushed most anything that got in the way. The copper-shod redoubts were teardrop-shaped or otherwise engineered to deflect tumbling boulders, but even those could not long withstand a direct hit from a major avalanche.
In the World Axis cosmology view, Malbolge was another huge cavern connected to Stygia by icy canals that ran hundreds of miles before reaching their destination. A former godly inhabitant had shaped the realm into a vast garden with fountains, towers, reflecting pools, and all manner of landscaping delights. With the coming of the devils, Malbolge was still beautiful on the surface but creeping corruption permeated the realm, twisting the beauty, perverting the architecture, and poisoning the pools.
Maladomini Maladomini, the Seventh Hell.
The Great Wheel cosmology view of the seventh circle of Hell described it as having vapor-polluted skies similar to Malbolge but the surface was solid.The post-Spellplague view described Maladomini as a colossal maze of passages each several miles across that eventually led to Cania, Malbolge, and Nessus. All three models agreed that the seventh Hell was filled with ruins of old cities, stagnant rivers, exhausted and abandoned quarries and strip mines, stone aqueducts and lava canals, decaying fortresses, swarms of biting flies, and black pools of ichor that erupted from the ground. The Lord of the Seventh was never satisfied with the construction of his capitol and repeatedly built and abandoned city after city. The largest and most beautiful was Malagard, a sprawling metropolis/palace/fortress/arcology with myriad black towers linked by a tangled web of bridges and walkways. Malagard was rumored to contain a million rooms and to cap an equally complex dungeon labyrinth.
Cania Main article: Cania
Cania, the Eighth Hell.
Both pre- and post-Spellplague cosmologies agree that Cania was a bitterly cold-dominant realm of solid ice mountains, titanic, unnaturally fast-moving glaciers, and nearly continuous snowfall that made Stygia seem balmy by comparison. Unprotected travelers were exposed to temperatures of −60 ℉ but on the positive side there were few creatures that hunted in the icy wastes.Earlier lore described the great citadel Mephistar as being constructed of iron but later reports say the Lord of the Eighth's fortress/palace was made of ice. All accounts seemed to agree the tower had a heated, luxurious interior and sat atop a gargantuan glacier called Nargus whose speed and movement were under the control of Mephistopheles himself.
Nessus Nessus, the Ninth Hell.
The ninth and deepest Hell was a land of extremes in the Great Wheel view: regions cold as Cania, volcanoes like Phlegethos, a lake of ice, a flaming forest, sheer cliffs, firewinds, and a citadel even larger than Khin-Oin in Hades (later, the Khin-Oin became part of the Abyss). The World Tree view did not contradict this description of Nessus but focused more on the blasted and torn landscape out of which rose Malsheem, the Citadel of Hell. It was said that Malsheem could hold millions of devils within its mountainous edifice, from the lowest warrens deep in the trench to the soaring spires miles above the tortured plane. The World Axis model agreed that a progression of rifts, pits, and chasms lead down and down, forming a vertical maze hundreds of miles deep that contained great cities, fiendish armies, and the mighty fortress of the Overlord Asmodeus.

Type

Ecumenopolis