The Primal Plane: A theoretical plane that possesses the archetypical qualities of all things found in all other planes. Also known as “The Original Plane” or “The Foundation of Reality”. There are no reports of anyone having ever visited or interacted with the Primal Plane.
The Ethereal Plane: An intangible and often invisible plane of existence residing infinitesimally close to the Material Plane, this is the most well-researched and understood plane beyond our own. The thaumatology of spells that influence and interact with the ethereal plane is extensive. This plane mirrors the material plane in geography, and is the cause, source and explanation for a wide variety of supernatural features such as auras, elementals and even a source of energy for spellcasting.
The Demi Planes: A realm of potential, this collection of planes contains pockets of reality that have been artificially created, carved out of existence by some power or agency. The spells Hide Object and Sanctuary are examples of spells that are capable of creating temporary, self-contained, unique territories within the Demi Planes. While few individuals have been able to master the spell of Planar Shift or similarly related spells, this is the plane with which they would interact.
The Demonic Plane: The plane where demons reside. Theories suggest that this plane is organized into a similar fashion as the Celestial Plane, but there is no anecdotal evidence to support this as few manage to travel to this realm, and none have been known to return from it.
The Celestial Plane: The plane where the gods reside. The plane is subdivided into dominions for each god’s realm. The gods have been known to bring mortals to their plane for short periods of time, but the mortal body is incapable of sustaining itself indefinitely upon this plane. Gaining entry to the Celestial Plane without being brought there by a deity is possible but exceedingly difficult.
The Etheric Plane: Also known as the “Plane of Dreaming” conventional knowledge suggests that this plane is unable to sustain any permanent physical structures. Mortals are unable to travel within this realm in their physical form, and it is usually only deities who traverse the Etheric Plane, and even then only with great difficulty.
The Transcendent Plane: The plane that the deceased eventually pass on to. Some beings reside for a time in the Ethereal Plane after death as phantasms, or in the Demonic or Celestial Plane if they had been closely associated with a deity in life. Eventually their souls will traverse the Etheric Plane, but once they pass beyond the boundary into the Transcendent Plane they will be unable to return to one of the lower planes. Even the gods do not know the nature of this final plane of existence.