A Plane of Existence is a usually finite dimension within the multiverse, often physically separate, but can be connected through portals, dimensional tears, and supernatural phenomenons, such as the River Styx. Many Planes can be accessed through the Material Plane, but other, more exotic planes require special methods to access, such as extraplanar travel, teleportation, or even death.
Material Plane Edit
The Material Plane is generally considered to be a "hub" in the multiverse, attracting all manner of people, beasts, and cultures. The Material Plane takes form as a vast, flat plane, made up of continents and even more vast oceans. The plane is bordered mostly by near impassable mountains, and waterfalls into the Abyss. Many other planes are directly accessible through the Material Plane, including the Feywild, the Astral Plane, the Wildlands, and the Abyss. Occasionally tears to distant planes will open on the Material Plane, however these tend to be destructive, and are more dangerous than helpful. However, tears have been successfully stabilized, and established as portals.
Astral Plane Edit
The Astral Plane is an endless, dark vacuum. The Astral Plane has no gravity, and no breathable air. However, many horrific creatures inhabit this plane, floating through the space in search of prey. Many planes, including the Elemental Planes are connected to, and exist within the Astral Plane, each with a unique atmosphere, most of which can support human life in some form. The Astral plane also merges with the Abyss at some undetermined point. Many planes exist as structures or large landmasses floating in space.
The Ethereal Plane Edit
The Ethereal Plane exists as an alternate Material Plane, filled with swirling fog and mist. The Material Plane is visible, but is extremely muffled, and blurry. Many creatures inhabit this plane, primarily specters, phantoms, ghosts and other creatures that can mask themselves in the fog. While on the Ethereal Plane, travelers are essentially invisible and ethereal on the Material Plane. The Ethereal Plane is easily accessible through the use of magic and portals are commonplace. Some natural sites exist as direct portals to the Ethereal Plane, and allow free travel between the Ethereal and Material Planes.
The Plane of Shadow Edit
The Plane of Shadow is similar to the Ethereal Plane. It appears as a dark, twisted version of the Material Plane, still blurry and muffled. The Plane of Shadow is not so easily accessed as its ethereal counterpart. This is an extremely hostile plane that few dare to traverse, and is home to all sorts of dark and twisted monsters. The Plane of Shadow can still be used as a way of reaching other planes, just a much more risky method.
The Elemental Planes Edit
The Elemental Planes represent the four major elements: Earth, Air, Fire, and Water. The inhabitants often have traits or features to reflect their home plane. All the Elemental Planes are connected in some way to the Material Plane, whether physically, or through a natural portal. They can be survived on, though some more comfortable than others, and each have developed settlements.
Plane of Earth Edit
The Plane of Earth is a dimension of solid stone and dirt. However, artificial caverns have been created to build cities and allow extraplanar travelers to survive relatively comfortably. A large amount of dwarves, humans, and gnomes have settled on this Plane.
Plane of Air Edit
The Plane of Air takes the form of an endless sky. Some magically constructed cities exist within this plane, and a large amount of the inhabitants can fly. There also exists vehicles that can travel across the endless sky. The Plane of Air stretches within the Elemental Plane and the Astral Plane. This plane is the most hospitable of the Elemental Planes.
Plane of Fire Edit
The Plane of Fire is a scorched, everburning world. Instead of water, there is lava, fire can rain from the sky. Yet the plane is home to the fabled Brass City, a large settlement ruled by efreeti. Fire Elementals are common, as are Azer, and other creatures with an affinity for fire.