The Planes

A plane of existence is a place within the multiverse that exists as its own pocket of reality. These planes are real locations, but they also embody spiritual and elemental concepts.
All of the planes represent some sort of spiritual or elemental principles.
No one is certain how they came about.
The planes of Dierde can be split up into a few categories.
The Prime Material Plane and its echoes, the Transitive Planes, the Inner Planes, the Outer Planes, and the Positive Energy Plane and Negative Energy Plane, all make up the vast space that can be explored.

The Material Plane and Its Echoes

Material Plane – Center of the multiverse where the vast majority of races live and where most adventures take place.
Feywild – Wondrous mirror of the Material Plane.
Shadowfell – Dark shadow of the Material Plane.

The Material Plane is where Dierde exists, in fact it is the same Crystal Sphere that once housed Toril.
The echoes of the Material Plane are the Feywild and Shadowfell planes. Both of these are echoes in the sense that they have roughly the same geographical layout as the Material Plane, but they are skewed in different ways.
The Feywild mirrors the Material Plane but makes all of its aspects more wondrous and mystical, while the Shadowfell is a dark reflection full of terrifying creatures and twisted images from the Material Plane. These echo planes each can have many smaller demiplanes within them known as domains of delight and dread.

The Transitive Planes

Ethereal Plane – Ghostly plane encompassing and touching the Inner Planes.
Astral Plane – Endless void encompassing the outer planes.

The Transitive Planes consist of the Ethereal and Astral Planes. While space, almost as we know it, exists within the Material Plane, these can be thought of as the “space” between the planes or as a way to travel between planes.
The Ethereal Plane encompasses the Inner Planes, while the Astral Plane encompasses the Outer Planes. The two are very different in composition, even though they are both immaterial expanses between worlds.
Those traveling through the Ethereal Plane will often find themselves in the “border ethereal,” which makes contact with the entirety of the Inner Planes. As such, someone using the Etherealness spell could walk unseen and unheard while still observing everything in the keep they’re surveilling.
Conversely, travel through the Astral Plane, and you’ll find what is largely a vast expanse of empty space. There are some places and even creatures that exist within this plane, but mostly it serves as a place for souls to travel to their resting spots in the outer planes. The Astral Sea is a part of the Astral Plane.

The Inner Planes

Elemental Planes of “ – ” – Planes that are the source and embodiment of the core elements.

• Elemental Plane of Air
• Elemental Plane of Fire
• Elemental Plane of Earth
• Elemental Plane of Water

Elemental Chaos – Swarthing pool of energy where the elements meet.

Beyond the Material Plane, the Inner Planes are the next most tangible concepts. The four Elemental Planes, Earth, Air, Fire, and Water, float within the Elemental Chaos and create a ring around the Material Plane.
While these are separate planes, they do touch each other. You can almost think of them like a color wheel with four primary sections. The places where they meet often characterize mixes of the elements: fiery storms, magma, steam, etc. While the great wheel shows this in a 2d visualization, all of the four planes do touch each other.
The closer these planes are to the Material Plane, the more they resemble it. Conversely, the further out you go, the more these planes become the pure embodiment of their respective element. The Elemental Chaos is one larger plane, almost like a Transitive Plane in its own right, that encompasses the meeting of all the elements in strange and volatile combinations.
Few Living creatures will make the Elemental Chaos their home, although there are rumors of several races of Elementals that have evolved to weather the extreme elements.

The Outer Planes

Arcadia – A place of purity where even such concepts as night and day or the different types of weather are never in conflict.
Mount Celestia – This great mountain is the home of justice and order.
Bytopia – Twin paradises representing balance.
Elysium – A heavenly plane filled with life and joy.
The Beastlands – An embodiment of nature’s beauty.
Arborea – The home of many elven Deities, this plane values strong emotions, be they rage, joy, or anything in between.
Ysgard – A place of eternal battle where the mightiest heroes go to test their might.
Limbo – Pure chaos and thoughts rule the form of this nightmarish plane.
Pandemonium – Those who travel here will surely be driven mad by the extreme weather, noise, and Darkness that rule it.
The Abyss – The many-layered home of demons. Each layer, of which there may be an infinite number, represents a different vile aspect of reality.
Carceri – An unforgiving prison plane that is home to traitors, backstabbers, and the like.
Hades – A gloomy plane that collects the souls of those not wanted by the Celestials of the Upper Planes or the Fiends of the other Lower Planes.
Gehenna – Home of the yugoloths, the most neutral of the fiendish races. A merciless plane that is also the birthplace of greed.
The Nine Hells – Archdevils watch over the nine layers of hell. This is home to possibly the cruelest deeds, as it is the embodiment of lawful evil.
Acheron – A plane of war split into four unending cubic layers.
Mechanus – Home to the modrons, the clockwork plane is likely the only place in the multiverse where perfect order prevails.

The Outer Planes are physical representations of abstract concepts. They can be split into the Upper and Lower Planes, embodying good and evil respectively. These are the planes that are furthest from the Material Plane in more ways than one. On our home Material Plane, everything exists in a state of shifting balances and conflict between opposing ideals.
In contrast, the Outer Planes are almost hard to understand for mortals. These are places where a single thought rules over existence. Elysium, for example, is full of such pure joy and perfection that it can be hard to leave. Mortal beings have a hard time pulling themselves away from such infinite beauty.
As far as inhabitants go, the many gods of the multiverse often reside among the Outer Planes. Creator gods and good-natured deities reside in the Upper Planes, while fiendish deities live in the Lower Planes. The servants of these gods too, celestials and fiends, can be found following their masters and fulfilling their purposes. Other beings may also reside in the Outer Planes.
Certain races that came to be in the far reaches of the Astral Plane or deep space, such as the githyanki, make their homes here, while others were created or formed with the planes themselves. Lastly, the souls of mortal beings find their final resting places among one of the many Outer Planes. Gods will lay claim to a soul based on the way that they lead their life.
Goblins, for example, are often claimed by Maglubiyet to fight in his eternal war on the plane of Archeron. Someone who suffered immense, undue pain throughout their life might be taken to Elysium by Ilmater, the broken god. Each of these planes have a wealth of lore to explore with many locations, artifacts, and characters just waiting to be discovered by adventurers. These planes aren’t the kind of place that you wander into at the request of some tavern-goer though.
The Outer Planes provide incredible challenges to anyone that might find themselves drawn there. The creatures that inhabit them harness great powers, be they magical or mundane.It’s for that reason that you probably won’t show up in one of these locales without some grand mission. You might end up in the Abyss to free an ancient hero or on Ysgard to collect a powerful artifact.
These sorts of quests are often in preparation for, or in reaction to, huge events which could have cataclysmic repercussions throughout the multiverse.

The Positive and Negative Energy Planes

Positive Energy Plane.
Negative Energy Plane.

Very simply, these two planes create the border that holds the entirety of the cosmos together. Within them are the very energies that provide substance to life and death within the Dierde multiverse. Like all of the other planes, they are building blocks upon which life can come into existence. But just as the Outer Planes are more conceptual than the Inner Planes, the Energy Planes are far more conceptual than any of the others. These planes are made up of almost pure energy in a way that’s difficult for mortal creatures to comprehend.

Other Planes & Domains

The Outlands was a plane that once existed in the same place as the Material Plane, but after the destruction of Toril (which would place it into its own orb as one of the 333 Gems of Tharizdun) it would become it's own plane on the edge of the Material plane and connected to the other plane. It

Informative Article on DND Beyond about the Planes