The Fragmenting of the World and the Nature of the Planes

The Fragmented Gem

That there exist planes of reality beyond our own is a truth known to all, though the minds of mortals by necessity must falter and fail to understand the true nature of their existence. Yet we may approach the truth such as we are able through an image.
Thus it is said among the very wise that in the beginning the world was like unto a gem, perfect in its unity and brilliance. But when the gods were removed from the world, that gem was broken into many fragments, rending the essential elements of reality asunder and forming discreet realms, which many have called planes, where these elements exist in distilled purity. It is said that the light of Being shines through each of these fragments, where it is refracted and tinted by the nature of each, until it is focused upon a single point of covergence at the Heart of the World, which many have called the Material Plane.
The planes are more varied and numerous than mortals may ever know. But there exist at various times and by various means what the wise call Thin Places, where the planes draw near to one another, and one may pass between them. Thus, we may begin to compile lore concerning certain planes, which may here be read.
The Planes

The Ether:

The misty otherworld which seems to lie as a cloth rumpled atop the material plane. This is the realm of ghosts and restless spirits. Featureless and barren, when one travels to the Ether, the Material Plane remains visible as through a thick fog, but only for a short distance.
The Feywild:

Roundabout where the fragmented light of being focuses to create our home, the Material Plane, it also sends forth two reflections, one bright, and one dim. The brighter reflection of our world is called the Feywild. This is a realm of florid beauty and strange fecundity. The golden sun of the Feywild never sets, nor does it rise, but ever bathes this realm in lavish dramatic beauty. Flora and fauna alike show forth in vivid color and splendid form. Where the border between our world and the Feywild is thin, features and landscapes of both realms bear some resemblance to one another. A copse of trees in our world may be a tall and thriving forest.
The Feywild is home to the Fey peoples and creatures, also called Faeries. Many Elves and Gnomes dwell here, as in the Material Plane. They are the most frequent travellers between our two planes. However, many other creatures may also be found in the Feywild. The nature spirits such as nymphs and dryads call this place home, as well as pixies and sprites, along with many others which I will not list here.
Sojourners to the Feywild are well-advised to be cautious. While it is a realm of great beauty, it is also a realm of great peril. Good and evil are not easily delineated in the Feywild. The ways and customs of its peoples are utterly strange to outsiders. Though their concerns may appear to be whimsical and childlike, to them they are gravely serious.
The Shadowfell:

The dimmer reflection of the Material Plane is the Shadowfell. It is the dark counterpart to the Feywild. This is a realm of darkness and decay. It is a colorless and barren realm. The sun is never seen in the Shadowfell. It is illuminated only by a dim and diffused gray, which glows darker than twilight. As with the Feywild, the Shadowfell bears some resemblance to the Material Plane where the border between them is thin. However, in this realm, the reflection is stained by death and decay.
Very little is to be found living in the Shadowfell. This is the realm where hungry spirits of undeath stalk and wail. It is the realm of shadows and wraiths. Hags and other dark fey creatures lurk in the inky darkness. Vampires have also been known to take up residence in this realm, as well as Liches and other dark sorcerers.
The Elemental Chaos:

This is a realm where the physical elements of the world are found in pure form: fire, water, earth, and air. Whether the elemental chaos is one plane or four, it is not known, for few who have travelled long here have lived to tell the tale.
This is where the elemental creatures dwell. Beings of pure enlivened matter.
The Astral Plane:

There is a facet of pure abstract consciousness known as the Astral Plane. It is an infinite swirling starscape. Here and there in the vast deeps of the Astral Realm fragments of matter hurtle through the nothingness: pieces of long dead demigods torn asunder when the earth was rent apart. Upon these islands in the Astral sea, some living beings have been known to take up residence, building extravagant structures of strange design. Creatures in this realm do not require food, drink, or air. Nor do they age. Gravity holds no sway there, and movement in any direction is as simple as thinking.

In the Astral Plane you will find chromatic rifts. These are cracks in the gem of reality that radiate in various shades and hues. Stepping through one of these rifts will transport a person to another plane. Wise travellers are able to navigate the planes by different colors with their desired destination.

Valoa:

Above the heretofor described planes there is a realm of paradise known as Valoa, home to the celestial beings like angels, unicorns, and couatls. As it is adjacent to the Outer Heaven, this plane is favored by the gods, and the very essence of that place is infused with the radiance and strength of their natures.

Valoa is an unfathomably vast and varied realm. At its heart is the towering mountain of the gods, Mt. Alvocar. Roundabout that peak are the cities of the angels, ringed by a peaceful valley of bliss. The lands of Valoa expand ever outward from that peak, rising into highlands, great forests, and wild crashing seas, the embodiments of the passion, life, and vitality of the gods. 

It is said that the spirits of the good ultimately find their way to Valoa, to dwell forever in its bliss. 

Myrkur:

Adjacent to the Void is the plane of Myrkur, the torturous realm of the enemies. Within Myrkur there are two regions: Hel and The Abyss.

Hel is where the devils reign. It is an empire of oppression and control. The devils are orderly in their wickedness, thus Hel is ruled by strict hierarchy. Though the devils wage constant war with their peers, they demonstrate strict fealty to those above them. Because absolute authority is the desire of every devil, they respect authority absolutely. Devils are cruel and ruthless. No act of depraved violence is beneath them. They are cunning. Foolish is the mortal who seeks to manipulate a devil. He will soon find himself caught in his own trap, forced into service or eviscerated for the enjoyment of his infernal master.

The Abyss is a realm of utter chaos, where demons and fiends of all kinds run wild. Whereas devils respect authority, demons respect only power. If a greater demon commands lesser demons, it is only because it can destroy them if it wishes. Their only desire is for destruction. Let the mortal who seeks to use a demon to his own ends beware, for he will unleash a force of pure wanton destruction upon the world.

Thanks be to the exalted ones that the powers of Myrkur have been kept at by for generations. May it ever be so.

The Outer Heaven and the Void:

Of the Outer Heaven and the Void, little can be said, for none have ever ventured to those strange places. Indeed, many say that these planes exist only as philosophical categories. 

It is believed that when Athaera separated the gods from the world, he set them in the outer heaven, while the enemies were cast into the Void. These constitute the space between the fragments of the gem of reality. From here the gods call out to beings in the world. Only the demigods, servants of the Exalted Ones, may pass from the Outer Heaven or the Void into the lower planes. 
Additionally, it has been theorized that those creatures known as Abberations originated in the Void, so strange and unseemly are they.