The cosmos teems with a multitude of planes and demiplanes, called The Universe. It encompasses the worlds where GMs of En run their adventures, all within the relatively mundane realm of the Material Plane. Beyond that plane are domains of raw elemental matter and energy, realms of pure thought and ethos, the homes of demons and angels, and the dominions of the gods.
Many spells and magic items can draw energy from these planes, summon the creatures that dwell there, communicate with their denizens, and allow adventurers to travel there. As your character achieves greater power and higher levels, you might walk on streets made of solid fire or test your mettle on a battlefield where the fallen are resurrected with each dawn.
The Material Plane
The Material Plane is the nexus where the philosophical and elemental forces that define the other planes collide in the jumbled existence of mortal life and mundane matter.
Beyond the Material
Beyond the Material Plane, the various planes of existence are realms of myth and mystery. They’re not simply other worlds, but different qualities of being, formed and governed by spiritual and elemental principles abstracted predating the ordinary world.
Planar Travel
When adventurers travel into other planes of existence, they are undertaking a legendary journey across the thresholds of existence to a mythic destination where they strive to complete their quest. Such a journey is the stuff of legend. Braving the realms of the dead, seeking out the celestial servants of a deity, or bargaining with an efreeti in its home city will be the subject of song and story for years to come.
Travel to the planes beyond the Material Plane can be accomplished in two ways: by casting a spell or by using a planar portal.
Spells. A number of spells allow direct or indirect access to other planes of existence. Plane Shift and Gate can transport adventurers directly to any other plane of existence, with different degrees of precision. Etherealness allows adventurers to enter the Ethereal Plane and travel from there to any of the planes it touches—such as the Elemental Planes. And the Astral Projection spell lets adventurers project themselves into the Astral Plane and travel to the Outer Planes.
Portals. A portal is a general term for a stationary interplanar connection that links a specific location on one plane to a specific location on another. Some portals are like doorways, a clear window, or a fog-shrouded passage, and simply stepping through it effects the interplanar travel. Others are locations-circles of standing stones, soaring towers, sailing ships, or even whole towns—that exist in multiple planes at once or flicker from one plane to another in turn. Some are vortices, typically joining an Elemental Plane with a very similar location on the Material Plane, such as the heart of a volcano (leading to the Plane of Fire) or the depths of the ocean (to the Plane of Water).
Transitive Planes
The Ethereal Plane and the Astral Plane are called the Transitive Planes. They are mostly featureless realms that serve primarily as ways to travel from one plane to another. Spells such as etherealness and astral projection allow characters to enter these planes and traverse them to reach the planes beyond.
The Ethereal Plane is a misty, fog-bound dimension that is sometimes described as a great ocean. Its shores, called the Border Ethereal, overlap the Material Plane and the Inner Planes, so that every location on those planes has a corresponding location on the Ethereal Plane. Certain creatures can see into the Border Ethereal, and the see invisibility and true seeing spell grant that ability. Some magical effects also extend from the Material Plane into the Border Ethereal, particularly effects that use force energy such as forcecage and wall of force. The depths of the plane, the Deep Ethereal, are a region of swirling mists and colorful fogs.
The Astral Plane is the realm of thought and dream, where visitors travel as disembodied souls to reach the planes of the divine and demonic. It is a great, silvery sea, the same above and below, with swirling wisps of white and gray streaking among motes of light of distant stars. Erratic whirlpools of color flicker in midair like spinning coins. Occasional bits of solid matter can be found here, but most of the Astral Plane is an endless, open domain.
Inner Planes
The Inner Planes surround and enfold the Material Plane and its echoes, providing the raw elemental substance from which all the worlds were made. The four main Elemental Planes—Air, Earth, Fire, and Water—and their four demiplanes form a ring around the Material Plane. Farther from the Material Plane, though, the Elemental Planes are both alien and hostile. Here, the elements exist in their purest form—great expanses of solid earth, blazing fire, crystal-clear water, and unsullied air. These regions are little-known, so when discussing the Plane of Fire, for example, a speaker usually means just the border region.
Outer Planes
If the Inner Planes are the raw matter and energy that makes up the multiverse, the Outer Planes are the direction, thought and purpose for such construction. Accordingly, many sages refer to the Outer Planes as divine planes, spiritual planes, or godly planes, for the Outer Planes are best known as the homes of the most powerful deities. When discussing anything to do with deities, the language used must be highly metaphorical. Their actual homes are not literally “places” at all, but exemplify the idea that the Outer Planes are realms of thought and spirit. Mortals perceive the energies of The Outer Planes and their inhabitants in a manner which makes sense to them, as familiar objects and recognizable beings such as perceiving Oakent as a great tree, when in fact Oaket vastly predates the concept of plants and is understood to represent the idea of a tree in its purest form.
Even in those perceptible regions, appearances can be deceptive. Initially, many of the Outer Planes appear hospitable and familiar to natives of the Material Plane. But the landscape can change at the whims of the powerful forces that make up the Outer Planes. The desires of the mighty forces that dwell on these planes can remake them completely, effectively erasing and rebuilding existence itself to better fulfill their own needs. Distance is a virtually meaningless concept on the Outer Planes. The perceptible regions of the planes often seem quite small, but they can also stretch on to what seems like infinity. It might be possible to take a guided tour of the Nine Hells, from the first layer to the ninth, in a single day—if the powers of the Hells desire it. Or it could take weeks for travelers to make a grueling trek across a single layer.