Building the Sandbox: The D&D Cosmology

I've been talking about the supposed "Ultimate Sandbox" for a decade now: the pie-in-the-sky project I've been working on that incorporates every official D&D product ever made into a single campaign.  I started it by piecing bits and bobs together as I read through D&D's history chronologically, but let's be honest here: I have nothing practical to show for it aside from some scattered notes.  And now that I'm factoring in the wider history of D&D outside of TSR, the progress I made has gone somewhat in reverse.  So with that in mind, I'm ready to start knuckling down and doing the hard work of turning this project into something practical.

So if I'm going to do that, I need to start with the big picture: the D&D planar cosmology and the various campaign settings that exist within it.  Using wikipedia, I'm going to list out all of the planes and settings, and give my thoughts on how they might fit together.

THE PLANES

For the majority of D&D's lifespan, its worlds have been contained with the Great Wheel Cosmology, as detailed in the chart below:

The Planes, as detailed in the Players Handbook from 1978.

From AD&D 1st edition to 3rd edition, this was the make-up of the planes.  It all starts getting odd from 4th edition onwards, and the Basic line did its own thing, but I'll deal with those below.  Let's go through the planes one by one.

The Prime Material Plane

This is where the vast majority of D&D worlds and settings reside.  The books have gone back and forth on whether there is one Prime Material Plane or many, but the answer is not particularly important.  What is known is that some worlds exist in the same universe, while there are also parallel timelines and alternate realities.  Our Earth, for example, is a parallel version of Oerth, the World of Greyhawk.  Some worlds are connected by a substance called the phlogiston, which can be traversed by magical ships called Spelljammers - Oerth, Krynn (the world of Dragonlance), and Toril (aka the Forgotten Realms) are three such worlds.  I would also contend that each world and universe has its own set of connections to the Inner and Outer Planes, and thus its own set of physical and magical rules.

The Inner Planes

These planes constitute the basic matter and building blocks of the physical universes.

• The Positive Energy Plane: Also known as the Plane of Life, it's been described as an "infinite, empty, blinding firestorm of life-giving light", and powers things such as healing spells.  Going to this place can still be deadly, though, as too much healing energy can make you explode.
• The Negative Energy Plane: The opposite of the above, also called the Plane of Death. It's an airless, featureless void of darkness that is inimical to all life.  Most undead seem to be powered by this plane in some way (particularly those that drain levels), as are some of the spells cast by evil clerics and necromancers.
• The Elemental Plane of Air
• The Elemental Plane of Earth
• The Elemental Plane of Fire
• The Elemental Plane of Water: Each of these planes is the elemental home of one of the four basic building blocks of physical matter in the D&D universe.
• The Para-Elemental Plane of Magma: The para-elemental planes exist at the places where the elemental planes meet.  The Plane of Magma exists between the planes of Earth and Fire.
• The Para-Elemental Plane of Ooze: Exists between the planes of Earth and Water.
• The Para-Elemental Plane of Ice: Exists between the planes of Water and Air.
• The Para-Elemental Plane of Smoke: Exists between the planes of Fire and Air.
• The Quasi-Elemental Plane of Radiance: The quasi-elemental planes exist where the Elemental Planes border the Positive and Negative Energy Planes. The Plane of Radiance exists where the Plane of Fire meets the Positive Energy Plane.
• The Quasi-Elemental Plane of Minerals: Exists where the Plane of Earth meets the Positive Energy Plane.
• The Quasi-Elemental Plane of Lightning: Exists where the Plane of Air meets the Positive Energy Plane.
• The Quasi-Elemental Plane of Steam: Exists where the Plane of Water meets the Positive Energy Plane.
• The Quasi-Elemental Plane of Salt: Exists where the Plane of Water meets the Negative Energy Plane.
• The Quasi-Elemental Plane of Dust: Exists where the Plane of Earth meets the Negative Energy Plane.
• The Quasi-Elemental Plane of Ash: Exists where the Plane of Fire meets the Negative Energy Plane.
• The Quasi-Elemental Plane of Vacuum: Exists where the Plane of Air meets the Negative Energy Plane.

The Transitive Planes

The Transitive Planes are those that connect the other planes, and generally contain little life.

• The Astral Plane: The plane of thought, memory, and psychic energy, devoid of space and time.  The souls of the dead pass through this plane on their way to the afterlife, and gods go here when they die or are forgotten.  The Astral Plane can be used to travel to the Outer Planes.
• The Ethereal Plane: The plane consists of two areas: the Border Ethereal and the Deep Ethereal.  The Border Ethereal connects the Prime Material Plane to the various Inner Planes, which can be seen as a grey haze from the Ethereal.  The Deep Ethereal is the birthplace of many demi-planes and "proto-magical realms", such as the Ravenloft campaign setting.
• The Plane of Shadow: A shadowy reflection that overlaps the Prime Material Plane, and can be used to cover vast distances.  In earlier editions its referred to as a demiplane, and by 4th edition it's been renamed as the Shadowfell.
• The Mirror Planes: Introduced during 3rd edition as an alternative to the other transitive planes.  They exist as a series of corridors that can be accessed by mirrors throughout the planes of existence.  Despite being presented as an alternative, I don't see why they can't coexist with the others, perhaps as a weird demiplane in the Deep Ethereal.
• The Temporal Plane: Otherwise known as the Temporal Energy Plane, or the Demiplane of Time. It's a place where physical travel can allow travel through time.

The Outer Planes

The Outer Planes are realms that embody the alignments, and are the homes of the gods. Souls go here after they have died.  The Outer Planes were mostly renamed for the Planescape setting during 2nd edition.  I suppose that those are the names used by residents of the Outer Planes, while the old names are more common on the Prime Material.

• The Seven Heavens: Also known as Celestia.  The plane of Lawful Good, and the home of various angelic beings such as archons, solars and devas.
• The Twin Paradises: Also known as Bytopia.  Exists between the planes embodying Lawful Good and Neutral Good.
• Elysium: Also known as the Blessed Fields, a realm the embodies the Neutral Good alignment.
• The Happy Hunting Grounds: Also known as The Beastlands. It exists between the planes embodying Neutral Good and Chaotic Good. It's a plane of idealised nature, inhabited by animal lords.
• Olympus: Also known as Arborea. A realm of passion, abundance, and capricious nature, the embodies the alignment of Chaotic Good.  The titans, the Greek pantheon and many elven gods reside here.
• Gladsheim: Also known as Ysgard or Asgard. It exists between the realms that embody the alignments of Chaotic Good and Neutral Good. A place for heroes to prove their valour, and the home of the Norse gods.
• Limbo: The plane that embodies the alignment of Chaotic Neutral. An alien plane of chaos, home to the frog-like Slaadi.
• Pandemonium: Exists between the planes the embody Chaotic Neutral and Chaotic Evil. It's described as an infinite network of pitch-dark catacombs, with winds that drive people mad.
• The Abyss: The plane of Chaotic Evil.  A horrible place with infinite layers, and home to hordes of demonic beings and evil gods.
• Tarterus: Also known as Carceri.  The plane that exists between those of Chaotic Evil and Neutral Evil.  A place where the souls of liars, cheats and traitors are imprisoned.
• Hades: Also known as the Grey Waste.  The embodiment of Neutral Evil, it's a place of hopelessness and the main battlefield of the Blood War between the Devils and Demons.  The Yugoloth (also known as Daemons) make their home here, as do the Greek and Norse gods of death.
• Gehenna: Exists between the planes that embody Neutral Evil and Lawful Evil. A plane of bleak eternity, also home to yugoloths.
• The Nine Hells: The Plane of Lawful Evil.  The Devils live here, including possibly Satan.
• Acheron: Exists between the planes that embody Lawful Evil and Lawful Neutral.  A place of pointless warfare, and home to the gods of orcs and goblins.
• Nirvana: Also known as Mechanus.  The plane that embodies the alignment of Lawful Neutral.  A clockwork plane that is home to the Modrons and Inevitables.
• Arcadia: Exists between the planes that embody Lawful Neutral and Lawful Good. A place of peaceful wildlands and kingdoms where all live in harmony.
• The Plane of Concordant Opposition: Also known as the Outlands. The plane that exists at the centre of the other Outer Planes, and embodies the alignment of True Neutral.  Sigil, the City of Doors, exists within this plane.

Other Planes

• The Far Realm: A place of cosmic horror that seems to exist outside of the other planes.  Exists as an excuse to use the Lovecraft mythos, basically.
• The Plane of Dreams: A plane far outside the others, usually not included in the standard cosmology. I'd be inclined to make this a part of the Ethereal Plane.

When 4th Edition Messed Everything Up

In a bid to simplify the above (or I don't know, just fuck around with it for the sake of things), the D&D cosmology was boiled down to six major planes in 4th Edition.  I gather that this was explained by cataclysmic events on the various worlds that this affected, such as the Spellplague in the Forgotten Realms.

• The Astral Sea: Pretty much corresponds to the Astral Plane from earlier editions.  Most of what used to be the Outer Planes now exist within the Astral Sea as "astral dominions".
• The Elemental Chaos: Corresponds to the old elemental planes.  Elemental Realms exist within this plane; the Abyss is one of them.
• The Feywild: A parallel wilderness realm that has aspects of the Positive Energy Plane and the Faerie Realm.
• The Shadowfell: An underworld realms with aspects of the Negative Energy Plane and the Plane of Shadow.
• The other two realms are The World, which is just the Prime Material Plane, and The Far Realm.

When 5th Edition Sort of Fixed It Again

When 5th edition D&D came out, it restored the old D&D cosmology and retained some of the elements introduced during 4th edition.  I'm not sure that this was ever explained (although I bet the Forgotten Realms came up with something).  The diagram below shows the current structure.  As far as I can tell, the biggest differences are that the Positive and Negative Material Planes encompass everything, the Shadowfell and Feywild have taken their place as Inner Planes, and the Elemental Chaos exists around the old Elemental Planes.

THE OFFICIAL D&D CAMPAIGN SETTINGS:

I'll run through all of the D&D settings below, and briefly discuss how they might fit into the above structure.

• Birthright:  Set on the world of Aebrynis, on the continent of Cerilia.  The players control divinely powered rulers, descended from those who were infused with the power of dying gods.  Seems like it should exist in its own universe in the Prime Material Plane, given that the  gods are no longer active there.
• Blackmoor: Dave Arneson's home campaign setting, and the earliest RPG setting of them all.  It's a realm rather than a world, and versions of it exist within various other settings.
• Council of Wyrms: A setting where the players can act as dragons.  It's set on Io's Blood Isles, separated from the rest of world by vast oceans. It could easily exist in the World of Greyhawk or the Forgotten Realms.  Io is a dragon god that explicitly exists in the Forgotten Realms, so I'd lean towards a placement there.
• Dark Sun: The post-apocalyptic world of Athas, with a heavy emphasis on psionics and magic that drains the environment.  Could be in its own universe, or possibly reachable by Spelljammer from other D&D worlds.
• Diablo: There were a couple of products in the late 1990s set in the world of the computer game Diablo, known as Sanctuary.  For consolidation purposes I'd love to be able to combine this with the World of Warcraft products below, given that they're both based on games by Blizzard Entertainment.  Something tells me that World of Warcraft lore is way too in-depth to allow for this sort of thing.
• Dragon Fist: This was promoted as a new game, and only ever released on the Wizards of the Coast website in the late 90s.  It was an AD&D variant, with some rules brought in from 3rd edition, which was then in development.  It's set in an oriental realm called Tianguo,  based on wuxia films and Chinese folklore.  It's only tangentially related to D&D, so I probably won't include it unless some offical D&D product dredges it up.  Perhaps I could just cram it into Kara-Tur somewhere, or stick it on the other side of Greyhawk.
• Dragonlance: D&D's first massively popular multimedia setting.  Set on the world of Krynn, with its many wars revolving around dragons.  It's one of the four major realms known to be accessible via Spelljammer.  Most of its products take place on the continent of Ansalon, but there's also a second continent called Taladas. 
• Eberron: A world that was introduced during the lifespan of 3rd edition.  I've never really got its deal. I guess it's like the industrial revolution but with magic?  It has a very different cosmology than other D&D worlds, but I'd consider those planes to either be demiplanes or smaller parts of existing Outer Planes.
• Exandria: Matt Mercer of Critical Role's campaign world, which was recently referenced in some D&D products.   Yet another world in the Prime Material Plane.
• Forgotten Realms: Ed Greenwood's home campaign (the existence of which predated D&D).  It's set on the planet of Abeir-Toril, and focused mainly on the continent of Faerun.  There's some weird jiggery-pokery with the worlds of Abeir-Toril breaking apart and joining back together that I've never fully grasped, but I don't need to get into that here.  It's one of the four major realms accessible via Spelljammer.  There are a number of sub-settings that exist within the Forgotten Realms:
• Al-Qadim: An Arabian Nights influenced setting in the land of Zakhara, south of Faerun.
• The Horde: Set in the Endless Waste, a Mongolian inspired setting between Faerun and Kara-Tur.
• Oriental Adventures/Kara-Tur: An Asian inspired land to the east of Faerun.
• Malatra - The Living Jungle: A setting to the south of Kara-Tur that was mostly detailed in Polyhedron magazine.  It's a jungle plateau based on pre-colonial Indochina.
• Maztica: A setting based on the pre-colonial American civilisations, set on the continent west of Faerun.
• Ghostwalk: Set in the City of Manifest, a gathering-place for ghosts which lies over the Well of Souls.  I'd be inclined to make this a part of Ravenloft, or perhaps put it in its own demiplane.
• Greyhawk: The world of Gary Gygax's home campaign, and the first official D&D campaign setting.  It was the default setting for 1st edition, and much of 3rd edition, and most of the classic adventures take place there.  It's one of the four major realms accessible via Spelljammer.
• Blackmoor: There's a version of the land of Blackmoor in this world.
• The Hyborian Age: TSR put out a few Conan modules, so I guess Hyboria counts as a D&D world.  Given that Gary originally based the Greyhawk continent of Oerik on the USA, I long ago posited that Hyboria could exist on the Greyhawk equivalent of Europe.  
• Jakandor: A self-contained island setting that's torn between tribes of magic-users and barbarians.  It could fit pretty well into either the World of Greyhawk or the Forgotten Realms.  I'd be inclined to favour Greyhawk given its pulpy vibe.
• Kingdoms of Kalamar: The World of Tellene, as developed by KenzerCo.  It's main selling point was its supposedly realistic geography and politics.  I remember seeing these books with official D&D logos on them, but I have no idea how Kenzer managed that.  I guess it's just another world in the Prime Material.
• Lankhmar/Nehwon:  The world of Fritz Leiber's Fafhrd and the Gray Mouser stories, and the subject of a number of D&D products.  It'll be another Prime Material world, possibly accessible via portal or gateway from Greyhawk.
• Mahasarpa: An Indian themed campaign of seven kingdoms, offered as a free web enhancement to the 3rd edition version of Oriental Adventures.  I'm inclined to place it on another campaign world, perhaps Greyhawk.  There are those realms on the other side of the world that Robilar adventured through after falling from the Greyhawk dungeons all the way to China...
• Mystara: The world of the B/X and BECMI D&D lines.  It's mostly set in a region called the Known World. A pretty generic high fantasy setting, although it has ascended immortal beings rather than gods.  Any differences to its cosmology can possibly be chalked up to demiplanes like I'm doing with Eberron.
• Blackmoor: A version of the land of Blackmoor existed in the ancient history of this world.
• Hollow World: A world that exists inside the globe of Mystara, similar to Edgar Rice Burroughs' Pellucidar.
• Savage Coast: A coastline area west of the Known World, inhabited by pirates and colonists, where a mutating curse is preventable only by wearing a special type of metal.
• Thunder Rift: A sub-setting for the revised D&D Rules Cyclopedia from 1991.  It's supposedly set somewhere on Mystara: the line's editor said it's on another continent,  but the author placed it in the mountains of Karameikos.  I'll go with the more specific placement.
• Nentir Vale: The 4th edition sample setting from the Dungeon Masters Guide, set in a vague world of fallen empires.  It's heavy on 4e stuff like tieflings and dragonborn.  It's possibly generic enough to cram into another setting.
• Pelinore: A setting developed in the UK via articles in Imagine magazine. Given its origin I'm thinking that I could perhaps use this world to house various other UK stuff, such as from White Dwarf.
• Planescape: This is set in the Outer Planes, and particularly in Sigil, the City of Doors.  This city lies in the Plane of Concordant Opposition, otherwise known as the Outlands.
• Ravenloft: The Demiplane of Dread, ruled over by mysterious dark powers.  This demiplane is split into smaller realms, each with its own cursed ruler.  The most famous of these is the vampire Count Strahd Von Zarovitch.
• Masque of the Red Death: A horror campaign set on 1890s Earth, which is already established as an alternate Oerth.
• Ravnica: The world of the Magic: The Gathering card game, a little-known fad from the mid-90s.
• Rokugan: This setting used for the 3rd edition version of Oriental Adventures.  It's also the setting for Legend of the Five Rings, though I'm inclined to just stick to the D&D books where that world is concerned.  I could possibly use it as one of the Asian lands on the flip side of the World of Greyhawk (which works given that Greyhawk was the generic 3rd edition setting).
• Spelljammer: Set in Wildspace, where magical ships known as spelljammers can be used to traverse the phlogiston to different worlds. Greyspace, Krynnspace and Realmspace, plus  the Astromundi Cluster, make up the four major regions of Wildspace.  I assume that some other  D&D worlds can be visited in this fashion as well, but not alternate prime material worlds like Earth.
• Theros: Another Magic: The Gathering world, based on Greek mythology.  It's amazing how such a short-lived fad could give birth to multiple campaign worlds.
• World of Warcraft: These were licensed and published by White Wolf, but they had the official 3rd edition logo on them.  Based on the ubiquitous video game property, obviously.
• Wilderlands of High Fantasy: The world described in the various Judges Guild products, which kinda sorta had TSR's blessing.  Generic fantasy but with a cool, weird 70s vibe.

OTHER PLACES

There are a bunch of other lands and settings that have been connected to D&D by anecdotes from the founders and articles in Dragon Magazine.  Some of these include:

• Nazi occupied Europe, which was adventured in by characters from Dave and Gary's campaigns.
• The American Old West, as depicted in the game Boot Hill. There are conversion notes for these rules in the AD&D Dungeon Master's Guide.
• Earth in the 25th century, as shown in the game Gamma World. Again, there were conversion notes in the AD&D DMG.
• The Starship Warden, from the game Metamorphosis Alpha. I'm sure Gary mentioned somewhere that his characters adventuredin the Warden.
• Edgar Rice Burroughs' Barsoom, on the planet Mars.  Several Barsoomian monsters are in the original D&D booklets.
• Wonderland, from the novels by Lewis Carroll, as depicted in modules EX1 and EX2.  Accessible through portals in the Greyhawk Castle dungeons.
• The world of Tekumel, from the game Empire of the Petal Throne. I'm not sure if any characters crossed over between these campaigns, but the rulesets are quite similar.
• The Isle of the Ape, based on King Kong.  Is this just an island on the world of Greyhawk, or another demiplane?  It's depicted in module WG6, and I believe was accessible through a portal in the Greyhawk Castle dungeons.
• The world from The Dirdir by Jack Vance.  Gary ran one of his kids through an adventure set there.
• The world of Frank Baum's Oz books. Accessible via one of the dungeon levels in the expanded Castle Greyhawk.
• Melnibone, from the Elric books by Michael Moorcock. Accessible via one of the dungeon levels in the expanded Castle Greyhawk.
• The world of the Dying Earth books by Jack Vance. I'm not completely certain about this one, but I'm sure I read somewhere that Gary ran adventures in this setting.
• Fomalhaut, a Lovecraftian realm accessible via a gate in Rob Kuntz's Temple of the Elder Gods adventure.  Possibly I'd connect this to the Far Realm, or just make it a demiplane.