Most adventurers travel the length and breadth of their land, facing an array of challenges from a variety of sources, such as monsters, dastardly villains, corrupt organizations, and even the perils of the landscape itself. These challenges, though daunting and difficult at times, are nonetheless rooted in the reality of the land around them. Magic can twist and distort to add an extra dimension to the challenges, but the scope of such power is necessarily limited by the hands that wield it.
These are all but a tiny fraction of the whole picture, however. They occur on the Material Plane, a sort of conjunction of extraplanar powers governed by invisible forces beyond the vision or even understanding of most people in the Material Plane. Beyond the boundaries of the Material Plane, what most accept as “reality,” the wider multiverse opens with an infinite array of options that stretches the boundaries of what’s possible – or breaks it entirely.
Beyond the Material Plane, a multiverse of adventure awaits… . A plane is broadly defined as any reality separated by metaphysical borders. They could be infinite or finite in size, but each plane is a self-contained dimension with its own laws governing existence. They usually cannot be accessed by physical means, though exceptions exist. Most of the known planes of existence are not inherently hostile to life, though again exceptions exist.
Planar Sages. A sage that specializes in planar knowledge. Think Volo, Elminster, Mordenkainen, etc.
Demiplane. A pocket dimension of finite size created from the raw protomatter of the Ethereal Plane. Certain spells can create demiplanes, usually as temporary locations, and some magical items access demiplanes as part of their enchantment. Many demiplanes can be accessed directly through a portion of the Ethereal Plane known as the Deep Ethereal but others are locked except through specific portals or gates.
Echo Plane. A reality “adjacent” to the Material Plane that includes some parallel aspects of the Material Plane, but usually not all. Each of these planes are an “echo” of the Material Plane that most planar sages believe are under the effect of a powerful exterior force. The Plane of Shadow is connected to the Negative Energy Plane while the Plane of Faerie is connected to the Positive Energy Plane. The other known echo plane is the Plane of Dreams, which contains a distorted version of the Material Plane affected by the dreaming minds of sentient creatures. The Ethereal Plane consists of two regions, the Border and Deep, and the Border Ethereal can be considered an echo plane as well.
Energy Plane. A plane that consists wholly or partially of pure energy. The two known Energy Planes are the Positive and Negative Energy Planes, which contain the source of radiant and necrotic energy respectively. These planes are hostile to life though accessible pockets exist. The Energy Planes touch the Inner Planes and Material Planes, creating regions of mixed aspect that generally can be visited.
Inner Plane. A plane that contains the source of one of the four basic elements of existence – air, earth, fire, or water. These are referred to as the Inner Planes because they form the nucleus of the multiverse itself, and on a metaphysical level are believed to be the core of all known reality. Each element is held within its own infinite plane, but the Inner Planes also “bleed” together, creating border elemental planes with non-opposing elements. Where air and fire meet, the Plane of Ash exists; where air and water meet, the Plane of Ice exists, and so on.
Great Wheel. The most commonly understood grouping of the planes understood by planar sages. Wheels, spheres, and circles are a common theme found amongst the planes of existence, so planar sages have connected the greater multiverse to the idea of the Great Wheel. At the center of the Great Wheel is the Material Plane, surrounded by the Inner Planes, and then orbiting around them are the Outer Planes. This is just one theory of the multiverse, however, and others exist that may be just as valid.
Layer. A subset of a plane of existence defined by different physical or metaphysical traits. Many of the known planes contain multiple layers, which function largely as separate planes themselves but connected to the broader plane by easier accessed portals and gates.
Material Plane. The plane of existence that sits at the conjunction of all the other planes. Also known as the Prime Material Plane, each Material Plane is comprised of elements from all the other planes, in varying degrees and amounts. They are infinite in size and scope and as varied as the rest of the multiverse, but they form the core of what most inhabitants call “reality.”
Multiverse. A generic term used to describe all of the known planes of existence. There are multiple theories of how the multiverse is connected together; the most common is the Great Wheel cosmology, but others exist as well.
Outer Plane. A plane of existence defined by a broad philosophical force. Most planar sages identify sixteen Outer Planes as part of the Great Wheel that correspond roughly to the intersections of good/ evil and law/chaos. An Outer Plane in this sense contains strong philosophical influence along these spectrums, which can include its absence as well. Mechanus, for example, is the plane of ultimate law devoid of good or evil, while the Abyss is the plane of ultimate evil and chaos. Some Outer Planes, especially the ones at the extreme, help those that align with it philosophically but rarely are they directly hostile to non-aligned travelers.
Transitive Plane. A plane that exists primarily as a means to an end. There are two known Transitive Planes – the Astral Plane and Ethereal Plane. The Astral Plane is a strange realm where time functions differently and serves as the connective “tissue” between all of the other planes of existence. The Ethereal Plane is considered a Transitive Plane as well though it only directly connects to the Inner and Material Planes.