Chronicles of Gaia
The Cosmos is a larger term for all of existence. The following are the primary known planes of existence and their relative location to each other.
Note that other minor planes may exist.
The Astral Plane
This is the great expanse in which all other planes of existence are suspended. Extra-dimensional spaces are widely believed to fixed points scattered far and wide throughout the Astral Plane, and some scholars believe that Gaia is just one of many such Prime Material Planes existing within Astral realm.
The Prime Material Plane
This is the physical plane of existence known as Gaia. It is a great curved quarter-dome, with the Seven Heavens above it, the Abyss in its base, and the Nine Hells below that. The Elemental Planes of Stone and Fire rotate above Gaia’s horizon, while the Elemental Planes of Air and Water rotate below.
The Seven Heavens
The Seven Heavens consists of multiple demi-planes stacked atop each other: The Waters of Heaven, Shadow Heaven, Knowledge Heaven, Nature Heaven, War Heaven, Light Heaven, and the High Heaven. Knowledge Heaven has an additional demi-plane called Mechanus, ruled by the ascended god Leonardo Mechanus, creator of the War Forged.
Note: I am going to rename each heaven into something much better. These are placeholder names for now.
The Seven Heavens are either a reward or punishment for fallen souls, depending on their choices in life and the ruling of Judex Maximus.
The Nine Hells
The mirror of the Seven Heavens, these nine demi-planes stacked atop each other are ruled by the Devils and Dragons. Like the heavens, they are either a reward or punishment for fallen souls depending on their choices in life and the ruling of Judex Maximus.
A sprawling underground labyrinth located within and below the Prime Material Plane (or Gaia). It houses the Ancient Demons, whose stirrings and diggings sometimes cause earthquakes or volcanic eruptions on Gaia. It can be directly accessed from Gaia should someone dig too deep.
The Elemental Planes
The four elemental planes rotate around Gaia.
The Elemental Plane of Fire; The Sun
The Sun is the Elemental Plane of Fire. Solaris is said to have conquered the Sun, pulling it across the sky for the benefit of those on Gaia.
The Elemental Plane of Stone (Earth); The Moon
The Moon is the Elemental Plane of Stone. (Referred to as Earth in game resources).
The Elemental Plane of Water
The Elemental Plane of Water rotates out of view below the horizon of Gaia.
The Elemental Plane of Air
The Elemental Plane of Air rotates out of view below the horizon of Gaia.
The Ethereal Plane
The Ethereal Plane is the realm of the soul, existing in the same space as and encompassing the Prime Material Plane, The Heavens, The Hells, The Abyss, and all four Elemental Planes.
Our souls always exist in the Ethereal Plane, with our consciousness and awareness only passing to that realm when our bodies lose their connection to the soul.
The Courthouse of the Dead, ruled by Judex Maximus, exists on the Ethereal Plane at the Apex of Gaia, and it is there that the dead go to be judged.
The Plane of Shadow
Not much is known about the Plane of Shadow, although it does run in co-existence with the Prime Material Plane. Most scholars agree that it is controlled by Umbra and the Triad of Shadow, although they are divided as to the degree to which it is itself a portion of the Shadow Heaven.