Cosmology of Terra Viejo

THE GREAT SPHERE It is believed beings known only as the Ancient Ones wrought the realm of Terra Viejo into existence from the primal energies of the void. At the center of a great crystal sphere they crafted the material realms of Terra Viejo, floating among the planes of elemental creation. Surrounding these material planes was a realm of energy, ideas, images, and sounds; the Astral Plane. Aside from mystics and sages, few people discuss the Great Sphere as anything other than a container for the universe. Indeed, the "Sphere" is often synonymous with the world of Terra Viejo, even though the material plane is but one distinct realm among many.
THE POSITIVE & NEGATIVE PLANES In creating the world of Terra Viejo, the Ancient Ones encased the material realm in a crystal sphere of the very forces of creation - positive and negative energy. These energies roil out from the corresponding poles of the crystal sphere like air currents. Violent maelstroms rage where their energies meet in the void beyond the Great Sphere.
THE ASTRAL PLANE When the Ancient Ones first created Terra Viejo and bound the primal energies of the void, they left the rest of the Great Sphere filled with a stillness thrumming with the power of possibility. This energy has no substance, but forms the great expanse that is found between the planes of existence. This is the vast emptiness of the Astral Plane.
THE DARK RIVER The Dark River was created by the gods as a path for souls to travel from plane to plane. The river flows through every plane of the sphere and is said to have a connection to Terra Viejo. Although the Dark River gets its name because the waters appear black as a moonless night to most travelers, it begins to shine as it passes through the upper planes.
OUTER PLANES When the "gods" withdrew from Terra Viejo during The Sundering, they gave form to the energies of the Astral Plane. The shaped these energies into realms divided into Upper and Lower planes, representing the moral inclinations of the immortal beings living within them. It is from these realms that they debate each other and engage in inscrutable schemes to enhance their standing, all while observing and manipulating the mortals of Terra Viejo.

• ELYSIUM In addition to being home to immortal beings of pure good, the realm of Elysium plays an additional role. It is on this plane that a "light shadow" of every living mortal walks about. These likenesses are constantly observed by guardian angels (usually devas), who record their good deeds, great and small, in enormous ledgers that they deliver to the gods of the dead when each likeness' corresponding mortal dies.
• HADES While home to immortal beings of pure evil, Hades is also a place of observation. Just as every mortal casts a light shadow of themselves into Elysium, so too do they cast a dark shadow into the realm of Hades. It is here that daemons watch them, whisper vile temptations in their ear, and record their crimes in dark ledgers to be delivered to the gods of death upon the demise of the likeness' mortal.
• THE ABYSS The most powerful of demons, the qlippoth, are like shadows of gods and beings of pure chaos. Using their incredible might, they long ago burrowed a pathway from the great void into the Great Sphere of Terra Viejo. Thus, the Abyss in which the demons reside is infinite, stretching out forever until it mingles with nothingness. They build themselves strange dark citadels in this realm and from them launch forces of chaotic destruction against the outer planes.

THE ELEMENTAL PLANES The elemental planes exist as a turbulent sphere of creation and even the gods who hold sway over the elements have little control over these spheres. Each one contains the purest form of the elemental energy and where their boundaries meet a violent mix of quasi-elemental energy bursts forth in elemental chaos.

• Plane of Water The plane of water is filled with its element, which flows with arcane currents, rippling with light or unseen in uttermost darkness. The Plane of Water is full of life, some of which finds its way into the material realm of Terra Viejo from time to time.
• Plane of Earth This plane is filled with every form of rock, dull and precious stones, dirt, sand, and the pure energy of the earth element. The creatures that reside here rarely come to Terra Viejo, as they lack curiosity.
• Plane of Air In this realm of elemental air, endless sky and strange clouds (made of condensed elemental air, not water vapor) host an array of flying and floating creatures. Some of them frequently visit the material world of Terra Viejo, but they're invisible or hidden in the world's clouds. 
• Plane of Fire The plane of fire is composed of blinding flames and smoke that erupts without a source. It's nature makes it hostile to beings that do not have special protections. While considered the least hospitable of the elemental planes, it is also home to one of the largest cities in the multiverse, the City of Brass.

THE MATERIAL REALM OF TERRA VIEJO Mortal races live on the material realm in the core of the Great Sphere, ensconced within the protection of the elemental planes of Air, Water, Fire, and Earth, though the material realm of Terra Viejo shares its place with other mystical energies, strange realms, and of course, all of the beings that dwell within.

• Material Plane of Terra Viejo Everything a normal mortal can see and touch is a part of Terra Viejo - the sun, moon, stars, land, sky, and water. With great magic, a person can see the Ethereal and Shadow Planes that coexist with Terra Viejo. With even greater magic, a person might travel outside the material realms, to other planes, communicate with their distant denizens, or summon them for worship or service.
• The Ethereal Plane Also known simply as "The Mists", this plane is a mist-filled dimension that exists alongside the Material Plane of Terra Viejo. It is a world that touches every part of the material realms and elemental planes. Those who venture into the Border Ethereal, the realm directly adjacent to a material or elemental plane, can look into the adjacent plane as if looking through a frosted window. However, the fog of the Ethereal muddle everything seen and heard in the neighboring realm. Travel into the Deep Ethereal is as if you were floating through a vast ocean of fog, with your vision almost completely obscured and no solid ground upon which to orient yourself. While the Deep Ethereal may be used to travel among the material and elemental realms, it remains dangerous and unpredictable with the possibility of arriving in mist shrouded realms of myth and legend only spoken of in whispers.
• Shadowfell Also known as the Plane of Shadow or Shadowlands, it is home to the dread and dark feelings that exist in life. To wander through this plane is to risk losing yourself in misery and apathy - why continue to fight the good fight when everything is meaningless and fleeting? This is not a realm that mortals visit on a whim, and those who do visit are forever changed by the experience.
• Feywild Also known as the Faerie Realm, this is the home of whimsical, cruel fey and endless desire. The call of the Feywild is difficult to resist and mortals are often willing to risk their lives to journey into it. Teeming with all manner of life, to walk the lands of the Feywild one courts death from all sorts of creatures and even if the perils of the land do not take you, it may be impossible for you to ever leave.

Some planar content taken from Stephen Bandstra's Introduction to the Planes