The Great Wheel cosmology consisted of a series of somewhat concentric spheres.
In the center was the Prime Material plane containing the phlogiston with the crystal spheres and worlds within, surrounded by an Ethereal plane (misty realms of proto-matter)..
Arborea or more fully, the Olympian Glades of Arborea, is a chaotic good-aligned plane of existence.
It is one of a number of alignment-based Outer Planes that form part of the standard Dungeons & Dragons (D&D) cosmology, used in the Planescape, Greyhawk and some editions of the Forgotten Realms campaign settings..
Unlike the Astral Plane, in which solid objects can exist (though are extremely rare) anything and everything that goes to the Ethereal Plane becomes Ethereal.
There is also something here called the Ether Cyclone that connects the Ethereal plane to the Astral Plane..
The Great Wheel was described as a complex, comparatively cosmopolitan place in which the gods of many worlds and pantheons mingled, the beliefs of many faiths and peoples bleeding together in a set of Outer Planes shaped predominantly by the polar forces of Law, Chaos, Good, and Evil..
Hades, also known as the Gray Waste, was the plane of neutral evil, home of the daemons.
The three layers of Hades were Oinos, Niflheim, and Pluton.
Pluton is sometimes mistakenly referred to as Hades..
Outside of the Prime and Ethereal were the Inner planes, also called the Elemental planes, which had their own structure based on a sphere.
Then came the Astral plane which connected the worlds in the Prime Material plane to each other (bypassing the phlogiston) and also to the last sphere, the Outer planes..
The only really significant difference between the Great Wheel and the World Tree is the absence of inter-planar connections in the World Tree cosmology (e
g connections from the Abyss to Pandemonium, etc )The World Tree also defines a few extra planes that easily folded into the Great Wheel planes
The term Great Wheel could refer to: The Great Wheel cosmology model from 1st, 2nd, 3rd (core D&D), and 5th editions
Tymora's realm, The Quarter of the Great Wheel, located on the plane of Brightwater in the World Tree cosmology model
The Great Wheel, seven earthmotes connected by bridges that
An early diagram of the World Tree cosmology
The World Tree cosmology model was outlined in the Year of Wild Magic, 1372 DR, and quickly became the most widely accepted model during those tumultuous times, supplanting the Great Wheel cosmology
