Those who have read the forum post at ENWorld linked to in the very first post of this blog can safely skip this entry - it's largely just copy-pasted from there. However, for those of you who have only read the blog, this will be totally new information, so enjoy!
What would eventually become the afterlife for Aarnian mortals is the Astral Sea, also known as the dream plane. This is the original realm of the fey before animals and legendary creatures were created. It is a place of unlimited possibility and much entertainment. It is also a place of horror and anxiety. When mortals were first created, they were given limited access to this place as they slept, in order to experience the primal energies of the soul and reduce the stress their minds encountered as they lived the material life.
Visitors to the core astral plane itself will most often experience it as an analog to a solar system (even if they do not know what a solar system is). In the center is an impossibly bright ball of fire, the core of the astral plane and the representation of the dream of K'tellos, the god of all fey. No astral explorer has ever attempted to enter this ball of fire and return, so very little is known of it or its contents. Orbiting the ball of fire are the 9 planes of hell, each represented by its own planetoid. Demons travel from plane to plane in jets, helicopters, hover-cars and other forms of aerial travel.
Interspersed everywhere else in this “solar system” are star clusters and wisps of glowing energy. The stars are short lived, with each one representing the dream of a sleeping mortal mind. When the dream ends, the star is snuffed out. Approaching a star or observing it closely allows one to view the dream of the mortal. Those who approach a star may enter it, and directly interact with the dream. If the dream ends while someone else is inside, the dream disintegrates around them, and that person then finds themselves floating in the astral ether, like they were before entering.
Clusters of stars are formed as dreaming mortal minds touch one another. Dreams of mortals may collide and intermingle, with two people sharing a single dream. The largest clusters are maintained by fey who have created their own home-away-from-home in the dreams of the mortals. Their clusters are so large that they are self-perpetuating, always having at least one mortal mind dreaming in order to maintain the cluster. In a way, these clusters could be considered demi-planes, stable worlds of dreams that have little impact on the rest of the Astral Sea.
The wisps of glowing energy are astral imprints of the noncorporeal undead trapped in the material realm. The material realm itself is not directly accessible through the astral plane without magical rituals, tunnels of energy or elemantic abilities, and this barrier works both ways. It is actually more difficult to access the material realm from the astral than to access the astral from the material, which can trap inexperienced astral travelers in the astral plane permanently.
Often confused with the astral plane is the "Inbetween," the ghostly ethereal realm. While astral bodies can be used to explore the Inbetween, it is an echo of the real world, and far more closely tied to it than tied to the astral. Those in the Inbetween see it as a grayish, cloudy version of the real world, with vague shadows where living corporeal creatures would be. Once a creature dies, its corpse can be seen clearly from the ethereal realm because it ceases to be the vessel for a soul, and becomes a mundane object. Creatures without true souls, such as mindless corporeal undead or magical constructs can also be seen clearly.
The Inbetween itself only exists by the will of the noncorporeal undead trapped in the material plane. If all noncorporeal undead were to suddenly cease to exist, the ethereal plane would vanish as well, along with the wisps of psychic pollution clouding the astral plane.