Cosmology

Not counting the multiple "layers" within planes, there are seven planes in total:

The Upper Tier
The Seven Heavens - the multi-faceted divine realm that is home to the Twelve Gods. These realms are connected to one another and to the mortal plane by rainbow bridges. Thus, to enter the Heavens, one must first find a rainbow. There are seven Realms within the Heavens, surrounded by the smaller Saintly Domains.

Castle Celestia
The mythical “city of stars,” this is the residence of the gods. The city is made of starlight and mortals are never allowed to enter.

The Radiant Isles of Elysium
This plane is strongly Good-aligned, and is the home of Rellia and Fentar.

The Wildlands of Arborea
This plane is strongly Good-aligned and Chaos-aligned, and is the home of Savra and Roxien.

The Eternal Battlefield of Ysgard
This plane is strongly Chaos-aligned, and is home to Magnus and Verne.

Saintly Domains
The various Saints of Firstworld are each given a small demiplane as their holdings in the Heavens.

The Material
Known to its inhabitants as Firstworld, this is the mortal plane we all know and love, coterminous and layered over and under the other three Middle planes. The Material is considered the “center” of the multiverse, and contains a single planet supporting life.

Constellations in the sky indicate which deities exist in the heavens above. During the events of Godsend, there are no stars in the sky.

Mirror Planes

 * The Feyreach: The realm of fey and home to the Kingdom of Faerie. Elementals are citizens of the Faerie Kingdom but cannot travel to the Feyreach. To enter the Feyreach, a mortal must travel there through a Faerie Ring or during a dance of the fey spirits. Fey have their own methods of travel.
 * The Ethereal Plane: A realm of positive energy and “improved” and “idealized” reflections. Life energy is said to stem from here. This realm is filled with mists and clouds, which exude a relaxing effect. Extracting magical energy from the Ethereal Plane is the core of wizardry – luckily, there’s an infinite supply. Entering the Ethereal Plane requires a mirror – often one can pass through it. Positive Energy stems from this realm.
 * The Shadow Plane: A realm of negative energy and dark twisted reflections of the features of the Material plane. Mortals tap into the Shadow Plane when they dream, their subconscious thoughts shifting the shadow-stuff like eddies. Familiars (tiny, insidious animals who do not cast shadows) are native to the Shadow Plane, and grant sorcerers and witches their spells. They can slip inside shadows to hide. Entering the Shadow Plane requires a shadow – stepping inside one to enter this realm. Negative Energy stems from this realm.

The Elemental Ring
Surrounding the Middle Planes but coterminous with none of them, an infinite ring of elemental energy stretches out, orbiting the plane with a steady rotation, as its influence brings about the world's seasons. The ring progresses from Earth to Ice to Water to Mist to Air to Smoke to Fire to Lava and back to Earth. It is from this volatile realm that Elementals spring. The shape of the plane defies mortal comprehension, and as one travels toward the "center" of the ring, it is possible to cross to the opposite side. The realm within the center is reliant upon where the traveler left. Traveling from water or fire leads to the realm of oil, and leaving from earth or air leads to the realm of dust. Fire brings about Summer, Earth brings about Autumn, Water brings about Winter, and air brings about Spring. During the appropriate season, caster level checks made to cast the appropriate spells get a +1 bonus. On the Solstice of each season, spells of the matching element are cast at +1 Caster Level.

The Underworld
A series of wastelands and hells connected by the River Styx, populated only by demons, fiends, and the dead. Waterways and channels are the gateways to the Styx, and all paths into the Underworld involve either water (to travel through the Styx) or fire (the more dangerous routes directly into the lower planes). The souls of the dead find their way here. Those who cannot pay the boatman are swept away by the currents, to be snatched up by demons or devils, or to slip all the way to the inferno. Charon will take souls with payment (not necessarily money – it can be stories) to the afterlife.

The lower one goes (to an infinite depth), the drier and hotter the planes get, culminating in a point where the planes are nothing but an inferno that consumes even souls. Even demons cannot go deeper. The fire, however, is rising…

The Hellspire
The planes within the Underworld take the form of an inverted spire, with the infamous Nine Hells forming the spire’s core in descending order of size (with the largest at the metaphorical “top” closest to the Material Plane), ruled over by devils and their leaders, the Archdukes. The nine hells are listed below:

(To be Completed)

The Abyss
Surrounding these planes are the infinite wastelands of the Abyss, populated by the chaotic demon races and their terrifying rulers, the Demon Princes. The farther from the “core” of the spire one travels (in planar terms), the more chaotic it becomes. Directly adjacent to the “spire” are the Gray Wastes, home to neutral fiends who often serve as mercenaries for greater fiends. These neutral beings have no leaders.

Navigating between planes in the Underworld is more linear and straightforward than in many of the other planes. The River Styx spirals down counter-clockwise as it descends, wrapping around the Hellspire as it touches each plane. While interplanar travel is the easiest method to travel in the Underworld, with the right equipment, one can travel on foot or by boat throughout the hellscape from one world to another.

The Warding Wall
The Warding Wall is a metaphysical barrier between the Material Plane and the Underworld, maintained by nature spirits and the elemental guardian gods. These spirits keep the wall in good repair. If it were ever to be damaged, fiends would be able to slip into the material plane.

The Astral Void
The Astral Plane is the timeless, eternal void in which the other planes rest, except for the three “Mirror” planes of the Material. These three are coterminous with the Material Plane, but not with the Astral. The Astral Plane is devoid of gravity and even time – no one hungers there, and one does not grow older while on the Astral plane. Time spent there does cause time to pass elsewhere, though at an unpredictable rate.