The Planes of Existence

The seventeen planes of the Great Wheel Cosmology model found in the Outer Planes:  

Nirvana/Mechanus

Nirvana was the plane of lawful neutral. It consisted of only one layer where everything was in perfect order: equal parts Light and dark, heat and cold, and equal measures of the four elements. The entire plane was filled with interlocking wheels 1,000 miles (1,600 kilometers) or more in diameter slowly turning in synchronicity. Each disk had its own gravity extending in a sphere around it, enabling the surface(s) of the wheel to be inhabited. Mystra once made her home here and Helm's realm Everwatch, Psilofyr's realm Mycelia, Amaunator's Keep of the Eternal Sun, and Hoar's Doomcourt were all on this plane.  

Arcadia

Arcadia was between lawful neutral and lawful good in alignment, known for its trees. The trees of Arcadia grew in neat forests and regimented orchards. The bark was either Copper, Gold, Silver, or Iron, and the never-falling leaves ranged from dark green to fire red. The fruit from these trees had magical properties like potions when consumed. Arcadia had three layers, Abellio, Buxenus, and a third layer of which very little is known, including its name. See the main article for information about the inhabitants and features of Arcadia.  

Seven Heavens/Mount Celestia

Seven Heavens, also called the Seven Mountains of Goodness and Law, was the plane of lawful good alignment, home of the archons. Its seven layers (Lunia, Mecuria, Venya, Solania, Mertion, Jovar, and Chronias) were joined in such a manner that traveling deeper into the plane became an ascending journey, up mountain after mountain for example. Each layer glowed with its own color of soft Light and each was unique in terrain. The Seven Heavens were the home of Bahamut, Yondalla, and Moradin Dwarffather. See the main article for information on the seven layers and their denizens.  

Twin Paradises/Bytopia

The Twin Paradises were between lawful good and neutral good in alignment. The two layers (Shurrock and Dothion) were described as hanging upside down from each other about 20 miles (32 kilometers) apart (from sea level to sea level), sharing the same sky. Gravity was normal for each layer but in opposite directions. The Twin Paradises were the home of Garl Glittergold, Baervan Wildwanderer, Segojan Earthcaller, and Flandal Steelskin of the Gnomish pantheon. See the main article for descriptions of each layer.  

Elysium

Elysium was the plane of neutral good. The wide, slow-moving, and mostly navigable river Oceanus flowed through all four layers (from Thalasia to Belierin to Eronia to Amoria) and then on to the Happy Hunting Grounds. Most habitation was along the fertile banks of the river, diminishing farther away. Isis, Ishtar, and Enlil all made Elysium their home. See the main article for more information on the layers of Elysium.  

Happy Hunting Grounds/Beastlands

Outsiders called it the Happy Hunting Grounds, but the native wildlife, most of which were sentient and capable of speech, called it the Beastlands and didn't take kindly to being hunted. This plane represented the ideals of neutral good but tended toward chaotic good. Each of the three layers (Krigala, Brux, and Karasuthra) was vast and densely forested, but included habitats for all manner of natural creatures: mammals, birds, fish, reptiles, amphibians, insects, invertebrates, and their giant varieties. Skerrit the Centaur god made his home here as well as the Beast Lords. See the main article for information on the different layers and the "faces in the clouds".  

Olympus/Arvandor/Arborea

Occasionally called Olympus, or Arvandor, Arborea was the plane of chaotic good, home of both the Greek and Elvish pantheons. The two realms coexisted on the topmost layer of the plane at the pinnacle of their respective realms. The main feature was Mount Olympus, a huge mountain that linked the Greek part of the plane with the Prime Material Planes where they were strongest. This astral landmark also extended to at least one layer each of Gehenna, Hades, and Tarterus. This plane's three layers were called, in Greek/Elvish, Olympus/Arvandor, Ossa/Aquallor, and Pelion/Mithardir. Tucked away in a corner (so to speak) was the realm of Nephthys. See the main article for more information about this fascinating plane.  

Gladsheim/Ysgard

Sometimes called Ysgard, Gladsheim was between chaotic good and chaotic neutral in alignment and was the home of the Norse pantheon (of which Tyr was a member) which, despite a tendency to chaotic behavior, effectively seized control of the uppermost of the three layers. Their realm gives the first layer its name, Asgard, followed by Muspelheim and Nidavellir. Like Mount Olympus in Olympus, the main feature of this plane is Yggdrasil, the "World Ash", a tree that has roots and branches in the Prime Material Planes where the Norse gods are recognized as well as Niflheim in Hades. Forgotten Realms Deities that made their home here were Selûne, Sharess (in her aspect as Bast), Marthammor Duin, and Eilistraee. See the main article for more information on Gladsheim.  

Limbo

Limbo was the plane of chaotic neutral, home of the Githzerai and the Slaad. This plane was supreme chaos: a twisting, quicksilver place filled with bits and pieces of rocks, trees, the four elements, entire landscapes, strong winds, and random pockets of liquid, solid, or gas. Intelligent beings could subjugate the environment around them, causing the chaos to settle into forms of his or her desire. It was believed Limbo had five layers but they were all generally the same. Leira, Tempus, and Fenmarel Mestarine made their home here.  

Pandemonium

Pandemonium was the plane between chaotic neutral and chaotic evil in alignment and had no native inhabitants but many that were either immigrants, exiles, marooned, or prisoners. The entire plane was made of passages and caverns seemingly carved from solid Rock by the constant howling wind and wind-driven rivers. Demons and quasits lived or hid here and shadow demons were plentiful. Talos made his home here, and temporary visitors included Loki from Gladsheim and Loviatar of Gehenna. See the main page for more details on Pandemonium and its four known layers: Pandesmos, Cocytus, Phlegethon, and Agathion.  

The Abyss

The Abyss was the plane of chaotic evil, home of the demons and a seemingly limitless number of other foul Monstrosities. The stronger sought to dominate the weaker and the weaker conspired to overthrow the stronger. It was estimated the Abyss had 666 layers but it could well have been an infinite number.   The first layer was called Pazunia (after Pazuzu, who was most often found there) or the Plane of Infinite Portals, or the Palace of 1,001 Closets. It was a barren land of dusty deserts scorched by a red Sun. See the main article for information on the myriad layers of the Abyss.  

Tarterus/Carceri

The plane of Tarterus was located midway between chaotic evil and neutral evil in alignment. Each known layer of Tarterus is described as a chain of glowing scarlet orbs stretching into infinity. Each orb of the top layer is the size of a Prime Material world and the orbs get smaller with each successive layer. The orbs of the "inner" layers can be imagined as nesting within the orbs of the "outer" layers like Matryoshka dolls. See the main article for descriptions of the known layers of Tarterus. The Companions of the Hall visited this plane in the novel The Halfling's Gem.  

Hades/Gray Waste

Hades, also known as the Gray Waste, was the plane of neutral evil, home of the daemons. The three layers of Hades were Oinos, Niflheim, and Pluton. Pluton is sometimes mistakenly referred to as Hades. The layers of Hades were called glooms for good reason; they were realms devoid of emotion, hope, and peace—grey land and grey sky throughout, with no Sun, moon, or seasons to break the monotony. Here Anthraxus ruled in his Mighty Fortress, the Khin-Oin. See the main article for descriptions of the glooms and their denizens.  

Gehenna

This plane was midway between neutral evil and lawful evil in alignment. Each of the four layers (Khalas, Chamada, Mungoth, and Krangath) were composed of mountains and smoky, burning volcanoes with no bases or peaks—everything was built onto or carved into the sides of these mountains and gravity was at a 45° angle with the ground. Deeper layers had less heat and volcanic activity until you got to Krangath which had no natural Light or heat. See the main article for descriptions of the layers of Gehenna.  

Nine Hells/Baator

The Nine Hells, also known as Baator was the plane of lawful evil, home of the devils. The nine layers were: Avernus, Dis, Minauros, Phlegethos, Stygia, Malbolge, Maladomini, Cania (spelling changed in newer sources), and Nessus, and each extended infinitely in all directions and had its own physical laws and properties of matter. The barriers between layers connected the lowest points of the upper layer with points very high above the surface of the next lower layer, regardless if there was a structure (like a mountain or tall tower) there or not. Some infamous and powerful beings made their home in Baator, such as Asmodeus, Mephistopheles, Baalzebul, Belial, Mammon, and Tiamat. See the main article for descriptions of the Nine Hells.  

Acheron

Acheron was located between lawful evil and lawful neutral in alignment and was a place where armies of the Outer Planes would come to do battle in the Afterlife. The four layers (Avalas, Thuldanin, Tintibulus, and Ocanthus) each consisted of huge blocks of hard black iron-like material the size of countries that floated through air, joining for a time and then parting again. While blocks were touching, a being could move from one block to the next. Gravity pulled toward the center of each block. See the main article for descriptions of the layers of Acheron and the few who lived or visited there.  

Concordant Opposition/Outlands

Concordant Opposition, also called the Friendly Opposition, the Outlands, Godsland, and simply the Land, was the plane of true neutrality. Divine realms on this plane included the Caverns of Thought, Ilsensine's realm; the Court of Light, Shekinester's realm; Dwarven Mountain, which was the realm of Dumathoin, Vergadain, and Dugmaren Brightmantle; Annam's Hidden Realm, Semuanya's Bog, Sheela Peryroyl's Flowering Hill, Thoth's Estate, Oghma's House of Knowledge, Silvanus's realm of Summeroak, Gond's realm of Wonderhome, and Ubtao's Labyrinth of Life.