The Grand Design

Okay, enough philosophy. The next question is, "How does the whole multiverse fit together?" Well, that depends on who gets asked. A Bleaker will say there ain't no scheme, while a Godsman will go on about innate celestial glory and the like. None of them will answer the question straight. Maybe the best thing to do is to get a hold of the Guvners and ask them. (Fact is, their answer's no better than anyone else's, but they like to put things into nicely defined categories, and at least that'll give a clear picture.) Their answer would go something like this:

There's three (remember the Rule of Threes?) basic divisions of the multiverse. Although they're all connected to each other in a variety of ways, it's easiest to picture each as separate from the others.


Information in this section is from "A Player's Guide To The Planes"

The Prime Material Plane

The Prime Material is just one plane, but it contains lots of individual worlds. A world may be only a single planet or it may be a complete system with planets, moons, asteroids, comets, stars and more. Each world is sealed like a bubble in its own crystal sphere, and that sphere is surrounded within an amber stream called the phlogiston. Isolated as their worlds are, most Prime inhabitants believe themselves to be at the center of the multiverse, and their world the only one in existence.

And here's a word of caution to arrogant planars: each Prime world is a unique domain, with its own environment and inhabitants. Travelling to the Prime without information about the destination is akin to casually jumping through a portal into an unexplored layer of the Abyss and expecting to survive. Though planars look down upon primes and their clueless ways, the Prime Material is as wondrous and infinite a plane as any, with places to explore. The worlds and occupants of the Prime Material contrast based on the current development of culture, science, magic, and natural evolution.

Inner Planes

These are the rings of the elements, the building matter of the Prime Material Plane. They're places of narrow-minded extremes, places whose very existence is devoted to a single substance to the near exclusion of all else. The plane of Fire is filled with fire and creatures of flame, the plane of Earth is filled with earth and rock-like beings, and so on. Of all the planes in the multiverse, perhaps none are more hostile to mortal life than these.

Except for the planes of Air, Lightning, and Steam, mortals can't safely breathe on the Elemental Planes. On the plane of Fire, air is superheated beyond all tolerance and filled with poisonous gases. The Planes of Earth and Water have no air to breathe at all; the Paraelemental Plane of Smoke chokes what air there is with thick fumes; and the Energy Planes simply have no atmosphere to speak of.
The Inner Planes also have no north, south, east, or west, and some don't have have up or down. "Up" is whatever direction a being decides. With this condition, normal compasses are useless, so a cutter needs an elemental compass instead. Without one of these magical devices or - and don't even hope for this - a good landmark to sight on, a basher's quickly lost.

None of the Inner Planes are purely all one element, though. Over the history of all time, little bits of elements have drifted loose and crossed the boundaries between the planes, until by now there are pockets of most element types to be found on all the others. Boulder-like islands of earth drift through the plane of Air, pools of water are held geode-like on the plane of Earth, lava-like patches of Earth float on the seas of the plane of Water. Pockets can be useful to travellers, providing a place to stand, air to breathe, or water to drink - all the basic needs. Their sizes and durations vary greatly, but pockets have been known to hold large cities from time to time.

On virtually every plane, travellers had better make special provisions for food and drink, as well. The Inner Planes have no inns, farms, plants, or game suitable to any but their own elemental denizens. Sure, a xorn'll insist food abounds on the plane of Earth, but that's true only for those who eat rocks and gems; any other poor sod had better pack his own lunch. At least on the plane of Water a body can get something to drink...
The best way to get around on any of the Inner Planes is to get a guide, because natives to the Inner Planes never get lost on their home turf. Even the simplest harginn knows which direction the City of Brass lies in. A sage blood knows to hire himself a native guide straight off, and he never bobs him in the end either.

Outer Planes

For a true planar, the planes means the Outer planes, the Great Ring. No other place has the same richness or the same tingle of power as any of the Outer Planes. They comprise the greatest of all the rings, each plane its own universe. Some have limits, others are infinite. Each plane is linked to those adjacent to it by fixed gates - folks call the path between them the Great Road. With a map to the gates, a body can travel the entire circumference of the Outer Planes. 'Course, that's provided the fiends don't get him first...

Where the prime-material worlds vary by natural, technical, and magical development, and the Elemental planes contrast by substance, the Outer Planes differ by morality. Each one is attuned to a particular alignment, and the berks and terrain within it subtly or overtly reflect that alignment. The powers choose their homes within the planes of their own alignments, too. Limbo is chaotic and ever-changing, Mechanus is rigid and organized, Mount Celestia is peaceful, and the Abyss is brutal and deadly.
Primes have different names for the planes, which comes from their own peculiar understanding of the multiverse - like the Twin Paradises, the Nine Hells, the Seven Heavens, Tarterus, Olympus, Asgard, Hades, and Nirvana. Don't be thrown by them. Also, try not to laugh at the sods when they use these tags; it's almost certain they would've gotten the names right if they'd bothered to ask folks who know better.

While it seems that the seventeen Outer Planes have little in common, that's only because most planars take for granted what they do have in common. First, a cutter can walk and breathe on most of the Outer Planes without spells, magical devices, or other pretections - that's a big change from the Inner Planes. Second, most all places have a clear up and down: Down's the earth under a basher's feet and up's the sky overhead. Third, most planes got a north and south. It ain't the same from plane to plane, or even from layer to layer' but it's still useful for getting around.
A prime shouldn't kid himself, though - the Outer Planes are different from any weak prime-material imitation. Compared to the Prime, everything's greater here. Mountains are loftier, glaciers colder, deserts hotter, and even the colours have an extra hue. Nothing on any prime-material world can ever quite match its counterpart on the Outer Planes. After all, what's a basher supposed to expect in the homes of the gods?

Another important thing that many of the Clueless don't realize is that a plane's not just a single place. It's got divisions and areas within it, and things can change from area to area. Planes are made up of layers, different worlds that all fall within the plane. Generally, each layer falls under the sway of a different power or group of powers, which accounts for often start differences in appearance.
In some places, like the Abyss, the layers stack up like a messy deck of cards, mostly on top of each other, with an occasional layer that sticks out where it shouldn't. On Baator, the nine layers form the tiers of a descending cone, perfectly regular to each other. Other layers are joined by rivers, bridges, or - most fantastic of all - great clockwork gears.
Within a plane, or even within a layer, there can be a lot of different realms. A realm is an area ruled by a power or group of powers, who fashion the land to suit their desires. Each realm can modify the physical laws of the land. Gravity, weather, and even directions are subject to the control of the local powers. Hence, it's usually easy for a cutter to tell when he's entered a new realm There's a shift in the landscape, one that matches the ideals of the new rulers, that's noticeable to all but the most addle-coved travellers.

The Outer Planes are divided into three main groups: the Upper Planes of Good, the Lower Planes of Evil, and the Boundary Planes of Neutrality. Here's a good piece of advice: The Lower Planes are the site of the ever-raging Blood War, the lawless conflict that's raged for eternity between the tanar'ri and the baatezu. They're not places the foolish can pass through and live.