"It is a plane out of phase.
It is a place of ghosts and monsters.
It is right next to you, and you don't even see it.
”
— Manual of the Planes
Cosmology
Great Wheel
In the Great Wheel cosmology model, the Ethereal plane existed adjacent to the Prime
Material Plane and connected it to the Inner planes (the Elemental planes plus the Energy planes). The Ethereal touched the Prime at all points that were located within crystal spheres through what was called the Border Ethereal. It was unknown whether the Border Ethereal touched the Prime in the
Phlogiston.
The non-Border region was called the Deep Ethereal. While in the Border Ethereal, a traveler could still see into the adjacent plane but only dimly and not very far, whereas those on the bordering plane could not see the traveler without magical detection. Verbal communication was not possible between the Border Ethereal and the bordered plane. The Ethereal was unique among the many planes in that an individual could exist in two planes simultaneously: the Border Ethereal and the adjacent plane.
A diagram representing the relative locations of the Border and Deep Ethereal, the Prime
Material Plane, and the Inner planes.
When travelers crossed into the Border Ethereal, they and all their possessions were converted to their Ethereal equivalents—
Metal became ethereal
Metal, flesh became ethereal flesh, and so on —allowing free movement (in most cases) in any direction through the solid matter of the adjacent plane. Since everything was permeated with ethereality, an air-breathing creature could breathe ethereal air and could not drown in an ethereal lake nor be crushed by an ethereal
Rock. However, not all in the adjacent plane was insubstantial.
Living things larger than one-celled animals generated an aura that radiated around them and prevented passage to their interior, so an ethereal traveler could not place a weapon inside a
Living creature where it would materialize and cause damage. A jungle would be an extremely torturous maze to navigate; it would be much easier to float above the vegetation or pass below its roots. Dense metals such as
Lead or
Gold also prevented passage of ethereal matter. And finally, some magic spells and alchemical mixtures could form an effective barrier.
Travel in the Ethereal and Border Ethereal was accomplished by force of will—you wished to go somewhere and you did, at your normal rate of movement. There was a sense of up and down but no real gravity existed. Objects released from possession would hover where they were dropped; it was impossible to fall in the Ethereal plane. To get to another plane, one had to pass through a curtain of vaporous color into the Deep Ethereal, then traverse that region until reaching the curtain that demarcated the Border Ethereal of the destination plane. Each
Inner Plane and demiplane had a curtain with a unique color. The Prime
Material Plane's curtain was
Turquoise. If the (usually magical) ethereal effect wore off while a traveler was in the Deep Ethereal, he would immediately be forced through a random curtain at a random location in the Border Ethereal and deposited on the plane which it bordered.
When you passed through a curtain into the Deep Ethereal, time slowed down to one tenth the rate it flowed in the Border Ethereal and the plane that it bordered. For every ten hours spent in the Deep Ethereal only one hour passed on the other side of the curtain. Metabolic and other natural processes slowed down also, so it did not feel like ten hours, when you crossed back through a curtain into a Border Ethereal you were only an hour older and an hour hungrier.
The Deep Ethereal swirled with large blobs of protomatter (imagine a cosmic lava lamp) which could form a demiplane when a critical size was reached. Powerful wizards, technologists, or demigods could also bend the proto-matter to their will and create a demiplane. These nascent planes might exhibit some of the characteristics of the Inner planes or the Prime, but with their own rules of gravity, material make-up, etc., and even support life. Most demiplanes eventually collapse into themselves and break up or merge with another Inner or Prime
Material Plane.
