In the beginning …
It started with the creation of the world, when the sky and the earth were one. As there was no sky or earth, as a result there was only an empty void. However, one day, a gap formed in the void. All that was lighter than the gap headed upwards and formed the sky. All that was heavier than the gap fell down to become the earth. Rain fell from the sky creating a great mire before a clear blue drop of life-dew fell, settled into the newly created swamp and grew into a great tree. The tree stood firm on the ground and pushed up the Sky. With each day the sky grew ten feet (3 meters) higher, the Earth ten feet thicker, and the tree ten feet taller. And the bubble expanded.
After a while the tree grew seed pods which, when they burst gave forth the Elements, time, positive energy and negative energy. However the release of all of those conflicting energies caused a huge explosion and the bubble that contained the earth and sky was blown apart - creating lots of little bubbles with their own little bit of earth and Sky. We live in one of those little bubbles. The energies coalesced to make the elements planes. The void that was left became the Astral, the Ether and Void Space. It is said that the tree is still there, invisible to most, stretching from the heavens to the hells, passing through the Astral and the Ethereal, and linking all of the bubbles together. The elements trapped inside our world bubble became the Primordial Powers, and between them they nurture all life on earth.
The First Age
Little is known about the first age. It is believed to have been a time when the gods walked on earth and were truly the patrons of their people. It is sometimes called the age of heroes, and is often believed to be a golden time of great learning. But in reality all real knowledge and understanding was lost during the long wait after the Gods War when people regressed, to the levels of barbarians, so they could survive.
The Gods War
After the eternal winter the great snake drank the sea, the wolf ate the sun, cows turned to lions and ate everything. The armies of the righteous, the chosen who had died in battle, those whose hearts were lighter than a feather, and those who had gone into the east with the sun were mustered and they fought together against the undead legions of the underworlds. Gods and demon giants fought to the death, then the fire came and the seas rose up. Everything was destroyed.
The Long Wait
Except that it wasn’t. The Tree of Life is indestructible – and life goes on. Some hid within the trunk of the great tree, others became as birds and flew to the topmost branches, others hid in the great ant mounds around the roots, and some took refuge in the well of knowledge (home to destiny and the fates). Many small groups survived to repopulate the world when it was healed. Creatures with Dark Vision most likely hid somewhere under the earth during the god wars, while those with Low Light vision may have survived nest like structures buried deep in leafy branches. However, they are all less than they were in the days that went before.
Note: Spells like Plane Shift, Shadow Walk, Create Demiplane and Planar Refuge made it possible to escape and wait out the apocalypse. Even some mid-level casters would have been able to escape, and presumably take their entourage with them. Each one is, potentially, a seed for the new tribe.
The Second Age
This is where we are now - and different people will tell you different things about this age - nothing is certain. You must form your own conclusions …..
There are only four planes of existence – T * he Astral Plane – Home of immortals and the source of Shards
The planes are all infinite. That means (for example) that each of the gods can create their own infinite demi-plane within the astral plane - and it still remains one thing. The same works on the Elemental Plane to allow infinite pockets of each of the elements (or demi-elements) to exist. (Infinity is both weird and wonderful)
Demi-Planes are not infinite, but can be so large that they appear to be. A deity’s home demi-plane will grow daily - think of Greater Create Demi-plane cast at god-level with a Permanency on it – literally at the god’s will. Elemental Demi-planes work in pretty much the same way. However, if it feels better to you call them planes and make them infinite. Play it as you will, the sages, alchemists and high priests don’t really know for sure.
The Astral Plane is also known as the 'Spirit World' Mortal flesh and blood can't live in the spirit world, although our souls go there when we die. Some mortal creatures can send their souls there, temporarily, through spells, runes and other magical means. The gods and great spirits live here, overseeing their charges on the physical planes. At one extreme are the demi-planes of hope and life (the positive planes) and at the other the demi-plane of despair (the negative planes) - but most of the gods make their homes in their own demi-planes somewhere in between. It is said that the River Styx connects all of these demi-planes together and, that if you can pay the boatmen, one of them will take you to the right place. NOTE: Positive and Negative planes are now in the astral – think of them as a type of spiritual energy rather than a physical energy.
The Material Plane is where the mortals live. It allows the combination of elements, spirit and mana that makes up a man (or a dwarf, or a tree, or any other living thing). For all we know, our plane might just be one of many demi-planes that make up the material plane. Plenty of opportunity for alternate-reality settings.
The Elemental Plane – is a roiling mass of raw element and elemental energy. However, like often clumps together with like and there are demi-plane like patches (or they might be actual demi-planes or even whole planes if that suits you). Any character travelling here should be very well prepared and protected. However, it also hosts The Well, home of destiny and the fates.
The Ethereal Plane is also known as the World Tree or the Tree of Life. Some say that its roots in the Elemental plane, it trunk passes through the Material and the branches and leaves are in the Astral – giving rise to the ‘sandwich’ map pf the cosmos. Others say that the Astral, Material and Elemental planes are woven together like the threads in a cloth, and that the Ethereal fills the gaps between. No one knows for sure. However, the one thing they do know is that The Ethereal is the source of Mana – the thing that drives life and magic.
The Well is also known as the Well of Knowledge, The Well of Wisdom and the World Well. It a Demi-plane located on the elemental plane among the roots of the world tree. Those that have ventured inside report that it is a plane of green hills and still lakes that is lit by fires floating in the sky, and that there are many gates here to the elemental plane. What is certain is that The Well is home to Destiny and The Fates who are all busy setting the destiny for Mortals of all shapes and sizes. Humans, Dwarves, Elves, Kobold, Orcs and all the other mortal races. Your destiny is not an end result, rather it is a path that you must tread - but how you follow it, what you make of it and the eventual destination are down to you.
Shards – The Shards of Divinity. When the Old Gods were destroyed their being, their divinity, was scattered far and wide – although most of it found its way back to the astral. Some was hoovered up by the new gods, some was absorbed the godlings or demigods who survived the wars. But most still lies scattered, or bound up in Divine Artefacts, ready to be absorbed by whoever is capable. Gods, devils and demons are particularly interested - but mortals can become Mythic IF they absorb enough shards.
Mana – The essence of magic. Most concentrated in the Ethereal Plane, mana drives spells and magical effects. Some beings - Gods, Demons, Magic Beasts, Sorcerers, Bards, etc – have an innate ability to harness mana and cast spells or create magical effects, without assistance. Others – Wizards, Magi, other arcane casters – learn long complex formulae that allow them to manipulate mana and cast spells. Still others, are gifted their power over mana by a deity.
Planar Portals – (do we want to call them that?) are naturally occurring wormholes between the planes. Small Portals (called Gates) can be created by powerful magic uses - but they are as nothing compared to the Great Portals. Some believe they are a natural phenomenon, others say that they are super-gates created by ancient gods. Who knows. However, beings entering one side of the Portal, come out the other side, and can thus travel between planes. Unfortunately, these portals are nearly always in a places that are difficult to get to or very well hidden. Some philosophers believe that each sun contains a portal to an elemental fire pocket, while each habitable world contains portals to the Ethereal, Astral and Elemental planes. One has even postulated that a wizard could create a world by creating the appropriate portals next to each other in outer space. There is even a school that thinks the whole of the material plane was created in just that way.