The Anima Engine

"We often describe the planes as wholly separate places, infinite and pure.However, we know that they are in fact none of these things. The city of Axis is known to be no more than 108 Units in circumference and although no mortal is truly sure how long a unit is, we do know that these planes are finite. If the planes are finite, they must end.
The writings of the great explorer, the Archmage Yendor describe the "transitional zones" as one plane gradually becomes another. Yendor was also the first to use the term "demiplane" to refer to these areas as "the area of transition incorporated aspects of both bordered planes but results in a place that is native to neither". 
One of the most interesting demiplanes is the demiplane of Metal, existing between the two inner planes of Fire and Earth. The plane of Metal is said to be frighteningly cold and lonely, with great prismatic spires stretching up into a starless sky. Occasionally great jets of fire will burst from the ground, melting and reshaping the land before it quickly solidifies again. 
This could also be a description of the Astral Plane, minus the occasional gout of flame. 
 
Yendor considered that this may be the way the Astral plane had come into being, and named this odd effect "The Astral Engine". This may seem a big leap, but consider the other demiplanes. The transitional zone between Water and Earth is a demiplane entirely made of and inhabited by oozes. Noone is sure where oozes originate, so could this plane be an "Ooze Engine"? The area between the Water and Air plane is a frozen landscape, and is the only known frozen plane in the inner sphere. I suggest that this could be the "Ice Engine" that's responsible for all ice-elemental creatures and spells. 
The concept of these engines allows us to make two deductions. First of all, we can work out where a particularly odd planar entity originates from by simply describing the kind of Engine needed to produce it. We see creatures of terrible destructive energy, and can easily deduce that these things come from the Engine between the Positive and Negative energy planes. 
Second, by inferring the existence of these Engines we can begin to map the planes like never before! If we know the planes must intersect at some point, then we can truly work out how they fold together in time and space. As we discover new Engines, we learn not only about a new subset of elemental creatures and effects, we also learn of one more border for that plane. 
Finally, one of my favorite implications of this theory. What of a hypothetical border of all major planes, both of the inner and outer spheres? Obviously traditional theory says this is impossible, as the Material and Positive Energy planes are both bordered by only one plane. But what if they were not? What if this "Anima Engine" existed, what would it be like? 
There are a few philosophical considerations on this topic, my own being the over-simplified "Imagine if a native outsider from every plane was to sit down at a tavern; what would that tavern need to look like?". The only good thing to come of this theory so far is the Anima Engine Bar and Grill in Yegg, which serves absolutely exceptional blackberry cider. However, I am hopeful."
 -Librarian Ashfallen "On the suggested improvements for the naming of alehouses, pubs and taverns" 
Alex's Note: It would not be for another full year that the party actually met Ashfallen. Good times.