The Elemental Planes are a subset of planes that exist within Akrylonor (in a cosmological sense). They are the source of the four elemental ethers, while also drawing ether from each other, along with the Magic Ether that emanates from the Fey Plane, and also exist between Akrylonor and the unknown source of Spirit Ether.
Comprised primarily of a single type of ether, unlike Akrylonor, the Elemental Planes have little variance in their environments or denizens. They have limited interaction with Akrylonor. The Dragons of Akrylonor originated within, and the Elder Dragons sealed the main point of crossing at the Mouth of the World. The Arcane Society opened smaller gates into the Planes as well, but those were sealed by the creation of The Shard. Since the destruction of the Shard nothing presently stops passage between Akrylonor and the Elemental Planes, but they hold little of interest to the people of Akrylonor.
The Planes are ruled by the Titans, and each populated by assorted denizens of various forms, though usually only a single sentient race that acts as servants, and Dragons, who oversee these slave-like minions (though are essentially also slaves themselves).
Air[]
Ruled by Syliniev, the plain of the air is a mass of clouds and empty space, with near invisible patches of dense air called firmament. The Daiannar, a race of humanoid beings acts as the Titan's minions. Similar in appearance to the elven races of Akrylonor, they're distinguishable by their filmy blue tinged skin and pupiless white eyes, as well as their ability to fly.
Earth[]
Vorgas rules over this realm of tunnels and caverns, below an inhospitable service of chasms and sheer cliffs. He is served by the Gorgrym, a race similar seeming similar to Akrylonor dwarves (Khazad having been familiar with them, obviously) although made of solid black stone, and capable of reforming their shape as needed.
Fire[]
Pharagol governs these plane of lava oceans and fire pits. Unstable islands of ash dot the burning mass, providng homes for the Eferin, a race of fiery sorcerers. A second race, the Xalameir, are lizard like creatures that live in the lava oceans amphibiously.
Water[]
Caddarog rules over the seemingly endless underwater terrain of the water plane. The Meraphim, a race of fish scaled humanoids dwell in small clusters built from underwater plants.