The Inner Planes

The Inner Planes, otherwise called the Elemental Planes, the Elemental Globe, the Energy Globe, or the Elemental Chaos, the Inner Planes include the many Elemental and Energy Planes of existence, as well as the Shade Realms, such as the Feywild or Shadowfell.

Overall Structure
The Inner Planes are laid out in two nested shells, the Elemental Planes(Depicted in red) and their corresponding Shade Realms(Depicted in blue). In essence, the Shade Realms are simply more grounded and tamed versions of the greater Elemental Planes. It would be most accurate to draw an infinite number of radial lines outward from the Prime Material Plane to connect with the outermost "globe" of Planes, but they grow so similar that their differences are irrelevant, and so close that portals and the like form wholly naturally there.

Elemental Planes
The Elemental Planes are places of pure elemental and magical energies. Their rules are very different from those on the material plane, and highly elemental to the degree of fucking with spells that get cast there. They are listed below;

Elemental Planes
The Pure Elemental Planes; These are unmanageable with unique and somewhat annoying rules to them. They don't often have much in the way of adventures or treasures to gain, but sometimes... Sometimes there's a point. Typically you'd want to go to their Shades though.

Elemental Plane of Air
The Elemental Plane of Air is an endless skyline dotted with occasional floating islands, the only presence of Earth on the plane, and thereby the only source of Gravity, the rest of the plane bearing wholly subjective gravity. It is universally attested to as the best place to fly in Nexus, though the practicalities of this plane are few, and the dangers are maximal, as a fall from any height on this plane is nearly guaranteed to be lethal, if you ever hit the ground(Usually in the form of a floating island) again. Occasionally floating islands will contain rare materials, however, so exploring the plane is occasionally quite rewarding.

Elemental Plane of Earth
The Elemental Plane of Earth is essentially a grand block of earthen materials, primarily substances like Dirt, Sand, and Flint, occasionally peppered by pockets of air, water, or the most dreaded of fire and lava. One would think it is a good place to get some mining done, if you can find an air pocket, but it's actually one of the worst due to the rarity of metals and minerals, which aren't purely earthen. Finding such materials is even harder than finding a needle in a haystack.

Elemental Plane of Fire
The Elemental Plane of Fire isn't what you would expect. Because these planes are neutrally-aligned, the fires of this plane are not hot or cold enough to harm, and not bright enough to blind, but bright enough to emit a very dim light. The real problem is the lack of ground to stand on. Like the Plane of Air, the gravity is subjective, unless you find islands of Earth within the flames. Now, that doesn't sound too bad until you remember that when earth and fire mix... The results are Lava, which kills, Ash, which can't support you and you will most likely suffocate on, and Metal, which often grows in sharp or pointy ways... Which kills you. Don't go to the plane of fire, there really isn't much for you here.

Elemental Plane of Water
The Elemental Plane of Water is much in the ways of the plane of Air or Fire. There is no surface, there is no floor, except for occasional pockets of Earth which drift through the plane, and aside from those pockets the gravity is nonexistent. Where the water grows more negative, the plane gives way to ice, with steam in the positive spaces. Unless one is after the purest ice or the strangest fish, there isn't much to the water plane.

Paraelemental Planes
Paraelemental Planes are the Planes between the Elemental Planes, combining many traits of both, but formed primarily from the combined elemental influences; the Para-Elementals. There are more uses to these than the pure elemental planes, but you still want to go to the Shades. Really.

Paraelemental Plane of Aether
The Paraelemental Plane of Aether is the mixture between Air and Fire, and it serves as a sort of parallel to the Quasielemental Plane of Radiance. Aether as an element is bright and facilitates seeing and breathing, but certainly not standing. Like the Planes of Fire and Air, this Plane's gravity is subjective, but unlike it's counterparts, there's virtually nothing to steer you towards not falling. Hope you can cope. Like the Plane of Fire, however, the entirety of the Plane is not hot or bright per se, but varies between gentle warmth and gentle chill, with pockets of superheating, supercooling, and death. Unlike the Plane of Fire, however, this plane is not bright... It just allows you to see. It's a bit strange seeing those concepts disconnected, but it is also through this mechanism Aetherlights work, so it's not completely foreign to most people.

Paraelemental Plane of Grass
Despite the name's suggestion, the meeting of Earth and Water doesn't only produce Grass. Instead, this Plane is filled with life of all sorts. People, plants, animals, and many, many other things. With little to no Fire or Positive Energy, there isn't much hear to allow sentience or full thought, but the things here live in unique and interesting ways. And hey, Gravity exists here in an objective form, owing to the fact that roughly half of this plane is made from Earth.

Lots of things here are cute and cuddly. Lots of things here are nasty and deadly. Not much of use can be found here, save for magical plants. Take the risk if you wish.

Paraelemental Plane of Metal
The meeting of Fire and Earth, as mentioned in reference to pockets in the Plane of Fire(Above) produces Magma, Ash, and Metal, Metal being the balanced aspect of the lot. All metals are combinations of mostly earth and fire, and mostly in rough balance with eachother. This Plane is literally all metal with occasional air pockets, and it's basically a bear trap waiting to kill you. Don't come here unless you're looking for some very exotic metals, like Adamantine or Orichalcum or something. You will almost certainly die.

Paraelemental Plane of Mist
The Paraelemental Plane of Mist is where Air and Water meet. There's no gravity here, surprise surprise, and also no way to see, as the mists obscure even the lights you bring to the plane. Have fun, there's virtually nothing here unless you want to meet insane storm and cloud giants. There aren't even fancy floating islands most of the time.

Shade Realms
The Shade realms are where the Elemental Planes are more grounded, reflections of the Prime Material in every sense. They behave nearly identically to the Prime Materials, but with a dominant element. They are listed below;

The Elemental Chaos
The Elemental Chaos is the transitive plane between the Elemental and Energy planes. It is coterminous with the elemental planes, though the various elemental planes are each separate planes. Like with other transitive planes, there is a sort of bleed between the planes and the chaos; This is why it is named the Elemental Chaos.

Connections to Material and Phlogiston
They connect directly to the Material Plane and Phlogiston, specifically bleeding into them in specific ways and connecting directly through portals.

While not a direct connection, it is worth mentioning that a highly specialized Spelljamming vessel could sail across and through the elemental planes.

Connections to the Outer Planes and Astral Sea
There are many connections between the Outer Planes and the Elemental Planes, some happening through transitional planes, some happening through direct connections(Such as the Plane of Radiance connecting with several of the Upper planes).