Cosmology

The material plane is surrounded by five planes, each based on one of the five elements - Earth, Water, Air, Fire, and Aether. These planes are sometimes referred to as the elemental planes and are said to be home to a wide variety of elemental creatures, spirits, and phenomena.
The Material Plane: The material plane is the world we know and inhabit, characterized by its solid ground, flowing rivers, gentle breezes, flickering flames, and vast, open skies. It is a world of physical matter, where life and death, growth and decay, are part of the natural cycle.
The Elemental Planes: The elemental planes are said to be planes of pure energy, made up of one of the five elements. Each plane is unique in its properties and inhabitants.
The Plane of Earth: The plane of Earth is a place of solid ground, towering mountains, and cavernous depths. It is home to earth elementals, stone golems, and other creatures that embody the strength and stability of the earth. The plane of Earth is associated with stability, groundedness, and materiality.
The Plane of Water: The plane of Water is a place of vast oceans, rushing rivers, and tranquil lakes. It is home to water elementals, mermaids, and other creatures that embody the fluidity and adaptability of water. The plane of Water is associated with emotions, intuition, and transformation.
The Plane of Air: The plane of Air is a place of swirling winds, gentle breezes, and raging storms. It is home to air elementals, sky giants, and other creatures that embody the movement and communication of air. The plane of Air is associated with intellect, inspiration, and communication.
The Plane of Fire: The plane of Fire is a place of intense heat, flickering flames, and burning ash. It is home to fire elementals, salamanders, and other creatures that embody the passion and transformation of fire. The plane of Fire is associated with energy, purification, and transformation.
The Plane of Aether: The plane of Aether is a place of pure energy, where the boundaries of time and space are blurred. It is home to aether elementals, and other creatures that embody the transcendence and spirituality of aether. It said that this was the birth place of the gods. The plane of Aether is associated with transcendence, spirituality, and connection.
The Interaction of the Elemental Planes: While each plane is distinct, they are also connected and interact with one another. The material plane, for example, is said to be a combination of all five elements, with each element expressing itself differently in different parts of the world. Similarly, the elemental planes can influence one another, with the energies of one plane flowing into another.
Practitioners of magic and alchemy are said to be able to tap into the energies of the elemental planes to create powerful spells and potions. Elemental creatures and spirits can also be summoned and bound to do the bidding of their summoners.

The Ethereal Plane:

Said to be The Plane of Aether "bleeding" into all of existence, everything there appears to be made of a ghostly, translucent substance. Physical objects from the other planes, including creatures and structures, are visible in the Ethereal Plane but appear faded and insubstantial. Similarly, creatures and structures native to the Ethereal Plane are also visible but often difficult to discern from the misty background.
Traveling through the Ethereal Plane can be disorienting, as the landscape constantly shifts and warps around the traveler. In some places, the plane may resemble a dark and eerie wasteland, while in others it may appear as a peaceful and tranquil garden. Strange and otherworldly creatures also dwell in the Ethereal Plane, some of which are friendly to travelers and others that are decidedly not.
The Ethereal Plane is often accessed through the use of spells or magical portals, and those who venture into its shifting landscape are advised to be cautious. Travelers can pass through solid objects and even walk through walls in other planes, but they must be careful not to become lost or trapped in the misty, ever-changing landscape of the Ethereal Plane.
In addition to being a realm of adventure and exploration, the Ethereal Plane can also be a place of refuge and safety. Some creatures and spirits choose to make their homes in the Ethereal Plane, where they can escape the dangers of the other planes and its more physical threats.

The Hybrid Planes:

The Shadow Sea:

This is where the Plane of Water and the Plane of Air meet. This cold seemingly endless ocean is home to shadows and creatures of the deep. Not much is known about this plane of existence other than it is perpetually in twilight.

The Endless Wild:

This is where the Planes of Water and Aether meet. A vast variety of beast, vegetation, and Fey creatures call this plane home. It is a massive labyrinth of forest and plains brimming with life.

The EverCrests:

The EverCrest Mountains are where the Planes of Earth and Aether meet. Sometimes referred to as the 'The Towers of the Gods', it is said the the Gods themselves live at the highest peaks allowing them to see everything in all planes of existence. The way up is guarded by a number of earth elementals and large beasts that destroy or devour anyone who tries to ascend.

HELL:

Home of the 'Traitor Gods' that betrayed and murdered the All-Father. This is where the Planes of Earth and Fire meet. There is little refuge from the harsh, unforgiving environment.

The Profundum:

This is where the Planes of Air and Fire meet. The Abyss, the lake of fire, however one refers to it, it is a place of chaos and death. This is home of demons and far worse unknown entities. No one in their right mind would ever attempt to come to this forsaken place.

A depiction of the material plane surrounded by the five elemental planes and the five hybrid planes.