The Inner Planes - The Elemental Chaos

Between the Outer Planes and Terranon are what’s known as the Inner Planes. While not truly separate realms, pure elements crush up against each other and form vast tracts of the primordial soup that was left over from when Morwen created the world, infused with the remnants of the planes-that-were when Morwen’s cage was sealed.
Nominally ruled by Rhodena, though she rarely interferes with their rule, four primordial sovereigns (Air, Earth, Fire, Water), gargantuan elementals on par with the power of the most powerful demons and angels, give fealty in exchange for control over large swaths of their element. These primordials wage a constant war against each other, but their armies are in balance; they have never been able to get advantage over the other. Underneath these sovereigns, noble elementals called djinni (air), dao (earth), ifrit (fire), and marid (water) command the armies.
Where these elements brush up against each other, usually violently, para-elements form; elements that are a combination of two elements. Between the lands of earth and the sea of flame a vast range of volcanic mountains bleed magma. Between the ocean of water and the skies of air form a land of ice and snow under constant blizzard. Where the ocean of water meets the lands of earth, a vast swamp of mud oozes and swirls.
A person could travel across each of the planes, but doing so would take skill and extreme magical protection.
Dragons are believed to be intrinsically tied to the elemental plane, with each one serving as a direct conduit to the energies found there.

The Core Elements

The four elements of earth, fire, water, and air are the most common primordial elements in the Elemental Chaos. Two more core elements exist, but are no longer found in any great quantity: positive energy and negative energy. These quasi-elements are rarely found in pure form, but exist as mixtures within other elements, and are mentioned as part of the greater plane.

Plane of Earth - The Great Dismal Delve

Gravity: Heavy
Time: Slow
Shape: Finite (Where it meets another elemental plane)
Element: Earth
Ruler: Ogrémoch, Emperex of Earth (Tyrant of the Black Earth, the Mountain of Doom)

The Plane of Earth is almost entirely solid rock and soil pockmarked by bubbles of other elements. You may be envisioning a giant cave system through the earth, with tunnels that let you travel from place to place, but no. Teleporting to the Plane of Earth means that you are likely instantly buried alive with the weight of the entire plane crushing you. Solid does not imply stationary - the substances of the plane are constantly moving in a slow grinding motion punctuated by earthquakes and small tremors to massively violent upheavals. Caves and tunnels are filled in by the slow grinding rocks, unless action is taken to prevent it
While air may exist in scattered pockets, unbreathable gasses also exist, and unlucky travelers might arrive in a cave only to asphyxiate from lack of oxygen. Pockets of magma, water, ooze, or ash might also be encountered.
No light exists naturally on the Plane of Earth except for in those pockets of magma or rare luminous gems buried in the crushing darkness.

Magic

Magic acts a bit differently on the Plane of Earth

All earth spells are maximized.

You cannot control earth elementals summoned on the Plane of Earth without a second spell to bind them.

Air spells cannot be cast. The spell instantly fails.

Society

The dao of the elemental plane of earth have a very ordered and structured caste society of layers with very limited movement from the Great Khan down to the least miner. The least dao are still considered nobility above foreigners or other types of earth elementals, and many other earth elementals avoid the dao as much as possible or end up serving in the mines. The dao completely control the plane of earth, and there are no independent societies.
The Great Khan is the supreme ruler of all dao, and is only subordinate to Ogrémoch, the Emperex of Earth. Ogrémoch makes their lair within Stonemire Fortress on a plateau near the Fountains of Creation. They consider everything within the earth to be theirs, and they selfishly control it with an iron fist.

The Sevenfold Mazework

The center of all major dao activity within the Plane of Earth, the Sevenfold Mazework is an enormous labyrinth of tunnels, passageways, and chambers. Only the noble dao are immune to the confusion caused by the winding passages; even minotaurs, known for their ability to find their way in mazes, are not immune to the bizarre properties.
The Sevenfold Mazework is ruled by the Great Khan and his court of dao. They trade gems and metals throughout the planes

Quasi-Elemental Earth: Dust and Mineral

Pockets of Dust, infused with negative energy, exist within the Plane of Earth. These pockets are known to steal the life of any who enter, creating desiccated undead buried in the dust. These corpses are waiting to pull unwary travelers deeper into the pocket where their belongings will be leached into the soil, becoming dust again. Dust mephits and dust elementals are the most common living creatures.
Pockets of Mineral, infused with positive energy, are a miner’s dream. Large geodes form in these pockets, infusing the gemstones with magical energy. These gemstones are extremely prized for their ability to create light or capture spells.

Plane of Fire - The Crematory

Gravity: Normal
Time: Normal
Shape: Finite (where it meets another elemental plane)
Element: Fire
Ruler: Imix, Emperor of Fire (The All-Consuming Fire, The Eternal Flame)

The Plane of Fire is the most hostile plane, and without immunity to fire, you will die from the flames of this plane. Almost everything burns instantly here. Without immunity, the clothes that you wear, and the magic items you carry will instantly burn away, not even leaving behind ash; both the air you breathe and the land you walk is both on fire. The air you breathe is not oxygen, as that burns away almost instantly, but aerosolized rock and other toxic chemicals that are still burning. Where there is land, the land is formed from obsidian, scoria, and pumice and is surrounded by a sea of lava and pure flame. Below the sea of open flame is compressed liquid fire the consistency of lava, and below that is pure, solid, elemental flame.
The primary home of all fire elemental creatures, the Plane of Fire has a surprisingly vast ecosystem of creatures, including Ifrit, Azir, and Salamanders.

Magic

Magic acts a bit differently on the Plane of Fire.

All fire spells are maximized.

You cannot control fire elementals summoned on the Plane of Fire without a second spell to bind them.

Water spells cannot be cast. The spell instantly fails.

Society

The Plane of Fire has three major societies that are in conflict with each other. Notably, the King of the Azir, the Sultan of the Efreet, and the Grand Duke of the Fire Giants each rule over major sections of the plane and fight over territory and resources, with the Sultan of the Efreet controlling the largest portion.
Imix is passionate, quick to anger, vain, paranoid, and prone to jealousy. He always seems to have an endless supply of energy, which is spent on schemes that are always a detriment to others, especially the three countries he constantly manipulates. He is noted as a master technician and very creative, but his overconfidence and hautiness cause him to rush into situations and easily become frustrated when things don't go according to his plans.

The Crucible

Controlled by the Azir, the Crucible is a magical forge that is said to be able to forge the most powerful and legendary of items. Surrounding the Crucible are a number of lesser forges that the Azir use to create magical items for sale in the City of Brass.

The City of Brass

Controlled by the Efreet, the City of Brass is a major trade hub in the Plane of Fire. As one of the few places with breathable air and a livable temperature, many traders make their money from adventurers who want to explore the Plane of Fire or from natives who want to sell their goods outside of the plane.

Quasi-elemental Fire: Ash and Radiance

Pockets of Ash, infused with negative energy, exist within the Plane of Fire. These pockets create burning ash zombies and charcoal skeletons that seek out the living, only to suffocate it. Like its quicksand counterpart on Terrannon, pools of ash dot the landscape, ready for the unwary traveler to step inside. Ash mephits and ash elementals are the most common living creatures.
Pockets of Radiance, infused with positive energy, are some of the most beautiful locations in the universe. Bright auroras and colorful rings of light are ephemeral and fickle. These bright spots commonly have portals near Borealis. There are few native inhabitants of these Pockets of Radiance.

Plane of Air

Gravity: Light
Time: Fast
Shape: Finite (where it meets another elemental plane)
Element: Air
Ruler: Yan-C-Bin, Emperor of Air (the Shadow of the Four Winds, the Howling Hatred)

The Elemental Plane of Air is completely filled with air, but has various impurities that tend to form pockets or bubbles in the otherwise pure atmosphere. Gaseous bubbles include clouds of every type; fog, steam, mist, smoke, poison, acidic vapors, and the rare intrusion of elemental fire. Liquid impurities are usually water or water-based and tend to form floating spheres when not buffeted or frozen by the winds. Solid matter forms dust, ash, salt, or sand, and sometimes even chunks of earth approaching the size of a large asteroid. The larger chunks are often brought into the plane by intelligent beings and are very likely to be inhabited or formerly inhabited.
If you had to describe the Elemental Plane of Air in a single word, it would be “blue”. The very substance of the plane seems to radiate the magnificent sapphire hue of a clear summer day on Terranon. Visibility is twice what the best conditions could allow, unless of course, something obscures vision. Weather is the primary natural hazard on this plane; the winds are normally light to moderately strong throughout the plane, but can intensify into tornados, maelstroms, and hurricanes with powerful lightning. These extreme weather events are common, and when other elements get caught up in the storm, it could produce pounding rain, blinding snow, pelting hail, freezing sleet, and storms of choking smoke, biting sand, burning ash, scalding steam, or searing fire. The worst of these is The Maelstrom, a toroid-shaped tornado that has lasted for decades. Being caught in one is like being in a violent dust storm and death is only a matter of minutes away unless the victim is able to achieve escape velocity, perform an act of great strength, or receive outside assistance. Spellcasting is impossible within the maelstrom.
The Elemental Plane of Air is often considered the heart of commerce in the Inner Planes. Word is that those from the plane itself head to secret merchants in the Ethereal Plane for rare goods, but few know the truth of it and are willing to share the secret. The merchants are constantly looking for guards, especially those who can cast a flight spell or ride a flying mount. For those who can’t do either, this is the place to learn.

Magic

Magic acts a bit differently on the Plane of Air.

All air spells are maximized.

You cannot control air elementals summoned on the Plane of Air without a second spell to bind them.

Earth spells cannot be cast. The spell instantly fails.

Society

All djinn swear alliegience to the Grand Caliph in the plane of air, whose word is law, but he rarely leaves the capital in the Citadel of Ice and Steel to issue decrees. Instead, powerful Queens, Kings, and Sheikh rule freeholds - islands of earth and stone that are crammed with courtyards, buildings, gardens, fountains, and sculptures made of flame. Djinn do not require food and drink, but they love succulent fruits, great feasts, pungent wines, fine perfumes, shimmering silks, smooth satins, soft velvets, and other rich fare. The djinni government is fairly loose with few formal laws, but many djinn still see it as too restrictive, and often visit Terranon for the sake of respite from local lords and family. Aside from the noble djinn, there are many smaller independent settlements that only owe alleigance to Yan-C-Bin.
Although Yan-C-Bin rules the plane of elemental air as Emperor over all elementals, he typically leaves his followers to do as they please while he follows scholarly pursuits.

Citadel of Ice and Steel

Home to the Djinni of the Elemental Plane of Air, the citadel is actually a gigantic chunk of elemental ice and earth smoothed over time by the winds into a nearly perfect oval. The Great Caliph, ruler of the djinn, has his palace at the center.
The entire citadel is constantly free-falling, based on the caliph’s will. Thus, the only kind of movement possible within the citadel is flight.
Any creature incapable of flight or hovering is constantly buffeted by wind from djinn guards while they are in audience with the Great Caliph.
It is rumored that the Great Caliph, Husam al-Balil ben Nafhat al-Yugayyim, has overthrown Yan-C-Bin and claimed both the citadel and his power, as Yan-C-Bin has not been seen for some time.

Borealis

Borealis is a magnificent spherical structure built around a vortex of quasi-elemental Radiance. Extending from the core of the palace are nearly a hundred spires. These heights reach over 1000 yards and make the whole of it look like a spiky sea urchin or dandelion seed. No two spires are identical in color, and the whole of the color spectrum is shown. The palace appears to be made of stained glass, but the word is that the panels are actually solid light. No one knows what magic could even be employed to do such a thing. At the same time, no enemy has so much as cracked the place, making it clear that it’s stronger than it looks.

Taifun, the Palace of Tempests

Taifun is an immense palace of stone built upon a great floating mountain near a quasi-elemental node of lightning. Here, where the air lashes constantly at travelers, this citadel looms like a warrior’s worst nightmare. The shipyards that surround it add to its impressiveness. Spreading out in every direction from the towering stone walls is a spider web of docks, and tied to these are dozens of airships. Both the aerial armada and the fortress are ruled by a powerful air genasi named Haalifith.

Quasi-elemental Air: Vacuum and Lightning

Pockets of Vacuum are complete and utter voids. There are no distinguishable regions, areas, or realms. No creatures live here. They are areas of complete darkness that snuff out any light that is brought in. No past, no future, and no change, these places are representative of nothing at all.
The Maelstrom is the best known Pocket of Lightning within the regions known collectively as the Infinite Storm. These thunderstorms of various hues crackle with electricity and howling wind. No seas exist in these areas, and any rain cascades back into the tumbling storm of the Maelstrom. The “sky” to loosely use such a term, is always darkened with rolling thunderheads and the sound of crashing thunder echoing endlessly everywhere.

Plane of Water

Gravity: Subjective
Time: Normal
Shape: Finite (where it meets another elemental plane)
Element: Water
Ruler: Olhydra, Empress of Water (the Crushing Wave, Well of Endless Anguish)

The Elemental Plane of Water is abundant with life: native creatures born of the elemental nature of the plane itself, sentient water-breathing peoples, and most every species of aquatic life that could survive after being sucked through a vortex from their plane of origin.
There is no deep or shallow, no dark depths nor wavy surface; just an endless ocean that feels as if you are submerged several feet in any body of water on Terranon. There is no sun, yet the water dimly glows with a bluish green luminescence. Volumes of water at any temperature and salinity can be found if you know where to look or have a guide. Water becomes cold and forms icebergs as you near the Frostfell; water becomes brackish as you approach pockets of Salt; water becomes silty and slimy as you near the Swamp of Oblivion; water starts to boil as you approach pockets of Steam. The plane has all varieties of water constantly in motion, influenced by currents and tides. Life that depends on particular conditions flows along with their preferred environment or suffers the consequences. Impurities such as bubbles of air, chunks of earth, and even short-lived balls of fire could be found floating about due to vortices or the workings of powerful beings. Habitats and settlements typically form near sources of food and shelter, or near portals and vortices to facilitate trade.
Supporting the teeming life of this plane are corals and plants that made their way here and found purchase. Huge drifting three-dimensional reefs and loose spheres of freshwater grasses, kelp, and seaweed are home to myriad species and are fertile fishing spots. Travelers must keep in mind that large predators also know about these fishing grounds also, or they might discover just how bite-sized they actually are. Just like the oceans in Terranon, the Elemental Plane of Water seems to have no limit on how large some creatures could be as giant squid, aboleth, and kraken are known to prowl the plane.

Magic

Magic acts a bit differently on the Plane of Water.

All water spells are maximized.

You cannot control water elementals summoned on the Plane of Water without a second spell to bind them.

Fire spells cannot be cast. The spell instantly fails.

Society

Marids are culturally a vehemently independent and proud people, and most believe that they deserve to be the Great Padishah, ruler of the marid. Because of their strong sense of freedom and individualism, there is not a true "marid empire". Marids living on the Plane of Water are citizens of a wide group of mostly independent stronghold communities. These communities swear fealty to the Great Padishah, but more often than not, this is in name only. Every individual marid claims whatever titles they can get away with, including ones not recognized by the truely powerful noble marids - titles like atabeg, mufti, shah, beglerbeg, and khedive - creating a confusing heirarchy of titles and honorifics.
Olhydra, the Empress of Water, delights in creating dangerous and destructive manifestations of water. She is more a force of nature than the other primordials, though she does have a fondness for humanoids, much like a child has a fondness for burning ants with a magnifying glass. Other elementals flee or shelter in place against her fury.

Citadel of Ten Thousand Pearls

Located within the warm waters of the Elemental Plane of Water, this large circular coral reef sports bubbling air fountains, carpets of kelp, copper doorways, giant clams and schools of fish. Most of the citadel is easily accessible because of the wide door frames used by the giant noble marid, but many passages are only passable by small fish or marid in their water form. Shafts of sunlight illuminate patches of the Citadel. No area is unlit unless the Great Padisha wants it to be so.

Quasi-elemental Water: Salt and Steam

Unlike most places in the plane of water, quasi-elemental zones of salt, also known as the White Wastes, are places of dry, endless thirst that rapidly dehydrate any creatures containing water. This also includes water-related elementals, including ice para-elementals, ooze para-elementals, and steam quasi-elementals. Pockets of salt are surrounded by the blue ocean above, and miles of white desert terrain. Filled with the negative energy of death, and the life-giving energy of Water, the White Wastes keeps you alive. Even when you should be dead. Even when you want to be dead. Visitors trapped here find that fatal wounds won’t kill them, but are instead preserved with painful salt in the wound.
Pockets of steam within the Plane of Water, despite its namesake, are pockets of cool to warm mist, never getting hot enough to burn, and the natural glow of the mist provides a healthy amount of light. In some areas, the mist gets thick enough to asphyxiate, but this is rare. These are largely considered the safest areas of the elemental planes.

The Para Elements

Where the core elements meet, the para-elementals form. These are not considered true ‘planes’ as such, but are locations that have properties and denizens of both planes. Areas of para-elements are quite large and can cover the area the size of a mountain range.

Fountains of Creation

The Fountains of Creation are a vast mountain range of volcanos that start at the border of the Plane of Earth and extend well into the Plane of Fire, forming an arc around the vast Cinder Wastes. There are many floating islands of volcanic rock that have not yet fully liquified.
Lava flowing from the Fountains of Creation into the Plane of Earth form a region known as the Furnaces, where the dao inhabitants of the plane use the lava to power their forges. These mountains are considered to have some of the most abundant elemental vortices of all the para-elemental, occurring in the heart of almost every active volcano.

The Great Conflagration

Little is known about the border between fire and air because of the vast wall of choking smoke filled with ash and soot. Even creatures immune to fire will eventually suffocate with prolonged exposure . A breathing apparatus can temporarily offer protection, but even magical methods tend to clog or fail. There have been unconfirmed reports of a higher number of negative quasi-elements in this area, making even airship travel perilous. Like the plane of air, there is no ground here, but there are more floating places to land. Unlike the plane of air, you’re just as likely to land on a thin shell of ash covering a ball of floating magma as on something solid.

The Frostfell

Located on the border of air and water, the Frostfell is primarily solid ice with vast caves of water and air. Not all locations on this floating iceberg are the same temperature; some locations are a balmy ‘frozen’ while others can only be survived with magic. As one of the most inhabited sections of the elemental planes, the Frostfell is home to ice giants, yetis, remorhaz and other cold-weather creatures as well as elementals like ice mephits.

The Swamp of Oblivion

One of the few locations that have connections with Faerie, the Swamp of Oblivion is a vast swamp filled with hags and twisted trees. There is no solid ground in the Swamp of Oblivion, and people have been known to throw powerful artifacts into the mud so that they’d sink virtually forever. The few communities that live here are built upon stilts, but eventually everything sinks into the mud, and the communities are constantly being rebuilt. The most common native bird here is the mosquito, and you would not believe the size of the elemental gators.