The world that mortals know and inhabit is just one of a multitude of dimensions, albeit arguably the most important or (at least) the place where all others come together in some way. Without the other planes, the Prime Material (as scholars call the dimension that the world resides in) would be a pale shadow of itself. Magic and life itself would be different, if they existed at all. On the other hand, without the Prime Material as the common bond between many of the other planes, they would be unknowably changed as well.

Travel to the other planes is somewhat rare. The Inner Planes are quite hostile to many kinds of life and the Outer Planes are difficult to reach even for brave, powerful, and well prepared adventurers. The Astral Plane is relatively benign, but also isn’t a very interesting destination in and of itself. And the Far Planes, even if they weren’t almost impossible to actually reach, are disturbing and uncaring to life as we know it.

What is far more common is for denizens of the other planes to come to this world (either on their own or by way of summoning) than for mortals to go to the others. Elementals, celestials, demons, devils, angels, and others all have their reasons for wanting to come to the world. It might be freedom, the chance at power, to honor ancient pacts, or something else. The minds of these creatures are frequently alien and their wants and desires difficult to understand by mortals.

Places where the boundaries between our world and other planes are uncommon, but not unheard of, and are often places of great potential power for those who have the knowledge to exploit it. The Inner Planes are the most likely ones to be found in this manner, causing such mysterious phenomena as geysers of blue flame, hills that ripple and move like water, winds that speak with a thousand voices, or rivers flowing through the air. As the Abyssal Rift proves, however, even the Outer Planes can juxtapose themselves with the Prime Material. Usually, these events rarely last more than a few days or weeks and might never return, but sometimes the connection is more permanent.

Inner Planes

Elemental Plane of Fire
Elemental Plane of Water
Elemental Plane of Earth
Elemental Plane of Air
The Para-Elemental Planes
The Astral Plane
Demiplanes

Outer Planes

The Nine Hells
The Grey Wastes
The Abyss
Arborea
Celestia
Elysium
Limbo

Far Planes
The Divine Realms