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Note that this "cosmology" isn't a campaign setting, for a single campaign setting is just one of the many lower dimensions in the Kosmos.
The Lower Dimensions
Any place within a single reality/universe/multiverse that contains all of its matter, time, and everything else, esoterically called "the demiurge". The dimensional layers are as follows:
0: Entropy, nothingness, the void, oblivion. It is ruled, though there is nothing and no one there to rule, by a non-being of nothingness, with no name. There are no inhabitants, though where it touches other dimensions pieces of it become umbrals, unelementals, void dragons, and other beasts of the void and nothingness. The death of immortals is thought to fuel the emptiness of the void.
- It's where you go when destroyed by a sphere of annihilation.
1-3: The three dimensions of Space, the bones of the demiurge. Watched over by the chioh ha qodesh Aditi, also known as Infinity, or even Lady Fate. She may be linked to the intelligibles in some way as both seem to share an interest in elevating mortals to divinity. Assiah is populated primarily by mortals, free thinking individuals given the ability to choose their own destiny. Though it is the intelligibles who are regarded as the guardians of Assiah.
- This is the Prime Material Plane, containing all the separate mortal worlds. Each world or planet is basically its own separate planar layer.
4: Time, the muscle and sinews of the demiurge that gives motion to its bones. It is the world of formation. The flow of time is dictated by the first one Zurvan, more commonly known as Father Time. His role is to deal with temporal anomalies and tampering by outside forces. Somewhere deep within are the guardians of time, the inevitables, who police the fourth dimension and are unswerving in their dispensation of the law.
- This is a catch-all term for all the transitive planes: the Ethereal (past), Astral (present), and Shadow (future).
5: Matter, the physical fundamentals (earth, fire, water, gravity, etc.), the skin of the demiurge that keeps the lower dimensions together, prone to corruption and pleasures. Ruled by the eldest elemental, known simply as Sin. For now he sleeps, but his dreams taint all who surrender to the left hand path. This is why most intelligent elementals tend towards evil.
- This is all the inner planes, from the negative energy plane to the paraelemental plane of wood.
6: Spirit, where demons, angels, and other spirit beings exist in their respective outer realms (for example: Heaven, Hell, Olympus, Asgard), the philosophical heart and soul of the demiurge. It is the most fractured dimension. Presided over by Metatron, the angel of judgement. As with many of the sidereals (cosmic gods), Metatron is currently deadlocked with one of the other fundamental forces of the multiverse. The great senschals of the spirit world are the angels, however over the eons their inherent goodness has been influenced by the other dimensions and now each distinct alignment has its own race.
- The outer planes where all the gods and devils dwell. Everything here used to be angels, until the dimensions cracked open and every dimension started to intermingle. That's why the so-called embodiments of Good are such jerks, and the fallen angels are now super mcnasty jerks.
7: Thought, the maddening far place, outside, the mind of the demiurge. It is the place of myriad thought, and is the most distant of the lower dimensions and the likely entryway point for extra-cosmic creatures. The most powerful entity of this dimension is named Limbus, though it has many names and more than many forms. Limbus seeks chaos and diversity in all things, and as such is in direct opposition to Zurvan. The pseudonaturals dwell here, insane thoughts twisted until they became real.
- This is, obviously, the Far Realm.
The Nth Dimension, or Dimension X, the barriers or space between the lower dimensions. Extra-cosmic entities lurk these spaces, hidden away before time.
The over-reality/surreality above any multiverse that contains all multiverses in one megaverse/omniverse. Though beings existent here are beyond such mundane concepts as time, space, and soul, in order to interact with each other in any way, they must operate under these crude fundamentals. The higher dimensions are as follows:
8: The Hoary Heaven, the place where all the sentient universes and beings of equivalent power reside. Most universes/demiurges are dormant, but when they "awaken" and become time lords (more on this later) their consciousnesses physically manifest here. The demiurges/time lords can be likened to a campaign setting, such as Mystara or Forgotten Realms. When they manifest you can punch them in the face. But I wouldn't recommend that to anyone who is less than ECL 3000 before taking on even the weakest one; these transcendental gods are MEAN. Their character sheets are basically page after page of separate I Win (Ex) special attacks and I Don't Lose (Ex) special qualities, which can only be countered by the right I Win MORE (Ex) and Oh Yes You Do! (Ex), which is why time lords and such really don't bother fighting anymore, and just sit there and let the pitifully irrelevant overdeities, gods, and mortals play around inside them without caring one whit about those bacteria. Manage to exit one and you can find yourself in another.
9: The Great Wall, which separates Muzaloth and Aravoth. Mirror-beings known as mazzaroth/spectrals challenge all who wish to break through the great wall to seek an audience with the Supreme Being (i.e. the Dungeon Master). In-game representation of the impenetrable DM screen.
10: The highest and final dimension, the dwelling place of the Supreme Being and former Supreme Beings. In here resides seven super-universes that "contain" all of Muzaloth; in this place, Kuvachim can be likened to seven hollow gems. This is also the home of the Akashic Library (i.e. the DM's books and campaign notes), which is basically everything in existence, the omniversal DNA.