The Four Major Elemental Planes

 The Elemental Plane of Air  The Elemental Plane of Air was filled essentially completely with air but had various impurities that tended to form pockets or bubbles in the otherwise pure atmosphere. Gaseous bubbles included clouds of every type, fog, steam, mist, smoke, poisonous clouds and acidic vapors; also the rare intrusion of elemental fire which is flame without fuel. Liquid impurities were usually water or water-based and tended to form floating spheres when not buffeted or frozen by the winds. Solid matter could be found here, from dust, ash, salt, or sand, to chunks of earth approaching the size of a large asteroid. The larger chunks were often brought into the plane by intelligent beings and were very likely to be inhabited or formerly inhabited. As described by the Great Wheel model, a traveler with a guide could approach the boundaries with the para- and quasi-elemental planes: where the whiff of smoke eventually became hot, thick, and choking, or the tang of ozone soon lead to heavy storms with arcs of lightning in all directions, or the temperature dropped until flakes of snow, crystals of ice, and lumps of hail finally became a wall of ice, or the light faded to gray and the air thinned out until there was nothing.

 The Elemental Plane of Earth 

The Elemental Plane of Earth was an infinite expanse of solid matter pockmarked by bubbles of other elements and riddled with fissures and tunnels created by burrowing creatures or the occasional small mining operation. Ensconced in a few of these pockets were trading outposts and the rare hidden wizard fortress. Solid does not imply stationary: the substances of this plane were constantly moving in a slow, grinding motion punctuated by earthquakes from small tremors to massively violent upheavals. Open spaces were gradually filled by the relentless shifting (or marauding earth elementals) unless action was taken to prevent it. Air could be found in scattered pockets but unbreathable gasses were also present—unprepared travelers lucky enough to arrive in a cavern might slowly asphyxiate while the unlucky quickly suffocated by being buried alive. Other pockets of magma, water, ooze, dust, or ash were particularly dangerous for miners if they accidentally breached one of these. No light existed in the Plane of Earth except for rare luminous gems buried in the crushing darkness. Travelers able to pass through stone were effectively blind unless they used magic such as a ring of x-ray vision, or until their ocular organs reached an open space where darkvision could operate or a source of light could be produced. Hearing was actually enhanced while encased in earth, to the point where travelers could detect any movement through the rock within a certain radius of their position.

 The Elemental Plane of Fire 

Arriving on the Plane of Fire was like stepping into the flaming maw of an ancient red dragon; if one didn't have protection or immunity from temperatures high enough to melt stone then death was swift. The following discussion assumes a visitor and all their clothing and gear had this capability and either did not need to breathe or could compensate for a superheated, often toxic atmosphere that could immolate one from the inside. In general, the more fluid the elemental fire, the hotter it was and the more damage it did to unprotected material.

Unlike the other three elemental planes, the Plane of Fire had normal gravity and a landscape, although most of the "ground" was made primarily of loosely packed elemental fire and felt like walking in a swamp of hot coals. The rivers and oceans were filled with a more liquid version of the same stuff and swimming worked normally as a mode of transportation. Non-native flying creatures found the atmosphere thin and therefore did not have their usual speed or maneuverability. Visibility was hampered by the smoke coming off the flames engulfing, but not consuming, nearly every solid, liquid, or gas (and creature) on the plane. What one could see was usually distorted by heat ripples. Geographic features such as hills, mountains, and cliffs did not have a geologic lifespan because even the more solid areas slowly moved like a subterranean magma flow as seen on the Prime Material Plane. Permanent physical structures were very rare.

 The Elemental Plane of Water 

There was no deep or shallow, no dark depths nor wavy surface, just an endless ocean that felt as if you were submerged several feet (say a couple meters) in any body of water on the Prime Material Plane. There was no sun, yet the water itself seemed to glow dimly with a bluish green luminescence. Volumes of water at any temperature and salinity could be found if you knew where to look or had a guide. The Great Wheel cosmology model explained this by the proximity to the para- and quasi-elemental planes: water became cold and formed icebergs as you neared the Plane of Ice; water became brackish as you approached the Plane of Salt; water became silty and slimy as you neared the Plane of Ooze; water started to boil as you approached the Plane of Steam. The World Tree cosmology described this plane as having all varieties of water constantly in motion, influenced by currents and tides. Life that depended on particular conditions flowed along with their preferred environment or suffered 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 elemental vortices or the workings of powerful beings. Habitats and settlements typically formed near sources of food and shelter, or near portals and vortices to facilitate trade.

Supporting the teeming life of this plane were the 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 were home to myriad species and were fertile fishing spots. Travelers had to keep in mind that large predators knew of these fishing grounds also, or else they might discover just how bite-sized they actually were. Just like a Prime ocean, the Elemental Plane of Water seemed to have no limit on how large some creatures could be as giant squid, aboleth, and kraken were known to prowl the plane. Small creatures could be deadly too, with poisonous spines or barbed tails. The smallest of them all was perhaps the deadliest: algae that formed the infamous "red tide". Exposure of the eyes or lungs to the red tide caused a blinding sickness as virulent as any disease.