Carceri

Tarterus, also known as Carceri, was an Outer Plane in the Great Wheel cosmology model representing alignments between chaotic evil and neutral evil. Situated between Hades and the Abyss, Tarterus was a plane of contention between the warring demons and daemons but few of those interlopers would challenge the native demodands. The Companions of the Hall entered Tarterus by means of the Taros Hoop in The Halfling's Gem.

Description
The six layers of Tarterus had a seemingly infinite number of worlds arranged like a string of pearls stretching into the air-filled void. In the top layer, Othrys, each orb was about the size of a Prime Material world and averaged about a hundred miles (160 km) apart. In each successive lower layer the planetoids grew smaller and farther apart. There was no sun but the soil of each orb gave off heat and a dull reddish glow, similar to the phosphorescence of fire beetles. The planets did not rotate and there was no day or night unless a greater deity wished it so in their realm. Seasons and weather occurred randomly and what little plant life there was would rapidly mature after rainfall and then wither hours later.

The barriers between layers were always located at the deepest points on each planetoid and always lead to the same sphere in the next layer, so the worlds of Tarterus can be imagined as spheres nested like Matryoshka dolls and each layer contained a string of orbs of a particular size.

Othrys
The first layer of Tarterus was named for Mount Othrys (from Greek mythology) which was really two mountains on two adjacent orbs (both also called Othrys) each about fifty miles (80 km) high joined together at the peaks in a massive citadel. The worlds of Othrys were so close together that a traveler could easily fly from one to the next. For those who did not wish to fly, the river Styx flowed through all the worlds of this level in the usual mystical fashion. Many other rivers fed the Styx, and the surfaces of this layer were mostly marsh, bogs, and quicksand. Othrys was the brightest (due to the proximity of equal-sized worlds on either side) and warmest layer; no worse than a hot summer day on the Prime Material Plane. Other than the mountains, the ground was soft, like peat, and cut by deep chasms. Othrys could be reached via the Astral Plane and had portals to the Abyss, Hades, and Concordant Opposition. Long ago it could be reached via Mount Olympus, but when the Olympian gods overthrew the titans they used their combined might to shatter the part of the mountain that connected to Tarterus, thus trapping the titans on this plane.

Cathrys
The planets of the second layer were smaller that those of Othrys and about five hundred miles (800 km) apart. Plant life in this layer was both abundant and deadly. The flora in the overgrown jungles and grasslands secreted acid that could eat through metal in a minute or less.

Minethys
The third layer of Tarterus had planetoids smaller than those of Cathrys which hovered about five thousand miles (8,000 km) apart. The air between orbs was torn by harsh winds which carried poisonous dust storms from world to world, making most surfaces a barren desert. Huge tornadoes periodically swept through, carrying anything in its path to distant locations or even an adjacent orb.

Colothys
The worlds of the fourth layer were spiked with colossal mountains rising above deep chasms. Hundreds of miles/kilometers from base to peak, the terrain of this layer made the orbs more asymmetrical than in other layers. Adjacent orbs were five hundred thousand miles (800,000 km) apart so they appeared to be small spiky red moons in the utterly black sky. Legions of demons and daemons made lairs in the canyon walls.

Porphatys
Black, acidic rain and snow assailed the many worldlets of the fifth layer from giant black clouds that moved between them. On individual worlds, islands barely higher than sandbars came up over the waves of shallow, cold oceans. The snow only stuck to the peaks of any mountains, melting to cover the rest of the surfaces with one to six feet (30 to 180 cm) of a weak acid that did not affect metal or stone but could eat away cloth in a minute or less. All barriers between this layer and the next were under water. The orbs of Porphatys were millions of miles/kilometers apart and barely discernible even when not blocked by demonic clouds. A pilotless vessel called the Ship of One Hundred endlessly sails the seas of Porphatys.

Agathys
The smallest, coldest planetoids occupied the sixth layer and were so far apart that neighboring orbs could not be seen at all. Every surface was covered in dark ice that showed streaks of red and the air was so cold it made breathing difficult. If any layer existed beyond Agathys, the barriers would have been buried under miles/kilometers of ice.

Inhabitants
The dominant race that inhabited Tarterus were the winged demodands. Shators were the ruling nobility, typically controlling major portions of an orb. All but the most powerful daemons and demons would avoid them. Also found on this plane were nightmares, achaierai, and shadow demons, with reports of mephits, hordlings, and vargouille.

Realms

 * Grolantor, god of the hill giants, made his home among the peaks and chasms of Colothys before moving to the World Tree cosmology plane of Jotunheim in a realm called The Steading.
 * Kiputytto, Goddess of Sickness and Mother of the Plague, was a goddess of similar portfolio as Talona and was either an aspect of Talona or was defeated by her in a battle over religious territory.
 * Malar the Beastlord had a realm in Tarterus before he moved to the World Tree cosmology plane of Fury's Heart called the Land of the Hunt.
 * Parrafaire's realm Trickster's Delight resided in Minethys.
 * Talona, Lady of Poison and Mistress of Disease, resided on this plane before moving to the World Tree cosmology plane of the Barrens of Doom and Despair in a realm called the Palace of Poison Tears.
 * Vhaeraun's realm, Ellaniath was located in Colothys before he moved to the Demonweb Pits.