The Universe is truely infinite.
It is made up of an infinite ammount of Multiverses, some of which are infinite.
Traveling from one universe to another is quite possible...
The Prime Material Plane, what we call "Alsatia," is a world like Earth in a universe like Earth's. It follows most of the laws of physics, after you include Magic and Gods, and it has Billions of Billions of stars, with other planets and such, out in space. The whole "Universe" (as we know it) is the Prime Material Plane, and it's not alone.
Coexistant with the Prime is Heaven, Hell, and Limbo, infinite planes aligned to Goodness, um, Evility, and Neutrality. All three are infinite (wheres the plane is Finite but expanding infinitely over time... Perhapse it is infinite 4th dimentionally...) and their borders (if you can concieve such a thing in an infinite plane) extend far beyond the reaches of Alsatia, and contain whole other universes like the Prime.
In Hell, every place in the prime corresponds to a place there, and, while they are not usually similar, they occupy the same space in a higher dimention. (The same way 2 objects can occupy the same point in space at different times, think dimentionally!) Those who were wicked in life are doomed to spend eternity in Hell in torment at the hands on it's Demonic natives. Souls in Hell are used as Currency, Building Materials, Food, Amusement, and Fuel. Those that are consumed, as food or fuel, are the truely lucky, for sweet sweet oblivion is their reward.
Heaven is a bit different, occupying the same space but functioning on a strange level. Everyone, dead or no, has their own personal heaven, that is perfect in every way, down to who's there, and even the existance of heaven itsself. People who have not yet died can be in Heaven, because, how could things be perfect without your children there to love you? This creates logical inconsistancies, but Heaven is, by deffinition, exceedingly difficult to comprehend. Mortals can barely wrap their heads around infinity; perfection is right out. Everyone who was good and pure, upon their death, rises to Heaven, to live in bliss for all time.. Unless eternirt doesn't suit them, in which case they can ecist as long as they wish before being either reborn or givingthemselves to oblivion.
Limbo is a strange place, misunderstood by most. It is mostly an empty expansive plane, only sparsely populated, and home to the souls of those not Good enough for Heaven nore Wicked anough for Hell. While Heaven is Bliss and Hell is Torment, Limbo is just, boredom. There is very little color, no flora or fauna, often nothig even to stand on. Some serve time and go to heaven, like a sort of Purgatory by Bordome, but most are doomed to boredom and frustration, either forgotten forever or harvested, eventually (once they're ripe), to be reincarnated.
Of all the Afterlife Destinations, Heaven is by far the least populated. Hell is next, it's requirements being quite a bit easier to meet, with Limbo taking the lead, as most people weren't terribly good or evil (though you wouldn't know it by looking- Limbo is, again, very empty!)
Within each Prime, and possibly all planes, there is an infinite number of 'dimentions', one for every decision and event throught the course of history, breaking the timeline into a causal tree of consequence. These 'alternate realities' are exceptionally poorly understood, but some people posit that Divination magics access these branches in reality to gather their information. (- Thus meaning that no divination is ever wrong, it's just reaching from an unconnected timeline.)
Other Primes exist, some within and some without the boundaries of Heaven and Hell, and these realities can be traveled to, as well, though little is understood about them. Some follow similar laws of existance to Alsatia, but others are very strange indeed, involving more or less than the 3 1/2 dimentions we're used to (1/2 for Time that functions Linearly only, like in our perception of reality). Existances on 2d planes, or in 6th dimentional paralells are possible, but their effects on creatures native to Alsatia are vague at best.
There are Elemental Planes, but they haven't been gone into in any detail. They may be whole Primes, unto themselves (which would explain why Alsatian critters have the Life type, and critters fromthe plane fo Fire have the [gasp]Fire[/gasp] type), orthey may simply be parts of Alsatia. Their true extent is unknown.
There is a Shadow Plane, a distorted mirror image of Alsatia, that is Coexistant with the plane. All things that exist here, exist there also, but.. Different... It could be saidthat Light is Shadow, Matter is Energy, Good is Evil, but that wouldn't truely describe the differences. People that have been there and returned have reported that it was often nearly identical, but the slight differences gave the whole place a dark, unwholsome feeling, like a cold wet veil draped over your face.
there are other planes that exist, but most of them are unknown or misunderstood. There is an Etherial Plane, but it seems most closely related to folds in the fabric of Alsatian space- Pocket Dimentions. Our understanding is limited at best.
- Kemrain the Theoretical Planar Physicist.