"They say that Carceri is the prison of the Gods.
Every world is the prison of gods and mortals alike.
They say that Sigil connects to every world.
This is true.
For Sigil is the true prison of gods and men.
All of us, we live within the Cage
Trapped in the domain of the Lady of Pain,
Who fears neither god nor mortal
And can be bested by neither,
For we exist as her playthings.
For she is Suffering Incarnate,
She is Samsara
And Suffering is beyond the power
Of Gods and Men,
Of Primordials and Demons,
Of Devils and Angels,
To bring to an end.
Or say they say.
But I say to you,
That One Who Walks the Nine-Fold Path
May Escape the Wheel of Rebirth
And Finally Put an End
To the Cruel Mistress of Sigil
To Samsara itself.
And then all will be free."
The Final Words of the Blind Prophetess Mari,
Before she died the Death of Dust
On the Streets of Sigil,
Year of Our Lady of Pain 375,874.
The world is a prison and a wheel, a wheel of rebirth. The city of Sigil is the focal point of creation; it somehow both surrounds and imprisons the world yet at the same time it is found at the very center, at the balance point between the realms of increasing joy above it and the realms of increasing sorrow below it. In some manner, it lies beyond the elemental planes which form the inner 'walls' of the birdcage which is reality, yet also inside them at the very center of the universe. It resembles a city built on the inside of a tube which swallows its own tail, a hollowed out donut. Attempts to tunnel out through the ground either result in something killing you or eventually you stumble through a portal into another plane,usually an elemental plane. The normal method, however, of egress, is the system of portals which connect Sigil to every other plane in the universe.
At the very top of creation is the Positive Energy Plane, the plane of total joy and bliss. A joy so total, it rapidly kills most lesser beings through too much happiness. At the very bottom of creation is the Negative Energy plane; it constantly draws down the power of the Positive Energy Plane through all of creation and devours it; unfortunate visitors are unlikely to last long before being devoured. Certain rumors claim that if you descend deep enough, you will get fired out of the Positive Energy Plane, beginning the cycle anew. But no one has ever been PROVEN to survive this.
Inbetween them are a series of planes, growing ever less blissful and more suffering and painful as you move down through all of the universe from the Positive to the Negative Material Plane. 'The Prime Planes', home to Mortals, tend to hover in the middle of reality, sometimes rising or falling during periods of greater hope or despair. Above them are the 'heavens', below them 'the hells'. As you move towards the elemental planes, planes become more purely elemental in nature, but also more attuned to order or chaos, depending on how orderly or chaotic the elemental plane you are moving towards.
The Astral Plane is a collection of rivers and oceans which flow out of the Positive Material Plane down through the Heavens and the Primes down to the Hells and finally cascade into the Negative Material Plane; it grows more and more dangerous as you move from the higher to lower planes, increasingly beset with hazards and monsters and finally plunging off deadly waterfalls into the Great Nothing.
Souls reincarnate according to Karma; those who do good rise upwards; those who do evil sink downwards. Those who are more orderly move towards the orderly elements; those who are more chaotic move towards the chaotic ones. Those born into higher or lower planes may be born into the ranks of the Celestials or the Infernals; those more orderly or chaotic may eventually become Modrons or Slaad or other similar beings.
The Gods themselves and the Demon Princes and Archdevils all were once mortal and moved up and down the ladder by their actions in many lives...or by finding shortcuts.
The Gods try to help mortals move up towards the Positive Plane and have easy access to power from it; thus they need not feed on mortal souls. The Demon Lords, etc, are far from that life giving power and thus must tempt and take mortals in order to find sustenance and sources of spiritual power to prevent their realms totally falling into the Negative Plane and being destroyed.
It is said that the purest souls will eventually join with the Positive Plane; the wickedest will be devoured by the Negative Plane.
The Primordials are ancient beings of unknown provenance; even they are not sure of their own origins. Some rumors claim that the Lady of Pain stole their power and memories and trapped them inside her cage, thus making herself the ruler of Creation. This may be true or they may just be another group of Gods or Demons with delusions of Grandeur.
Indeed, there's reason enough to believe some of the Demon Lords and Archdevils and Yugoloth Lords, etc etc were once Gods and some of the Gods may once have been Demons, who changed their ways, sinking down below or rising up. Certainly Asmodeus himself is said to have once been a mighty divine servant of a god who he betrayed and murdered, only to find when he usurped the realm, it plummeted from the heavens into the depths of the hells, corrupting him and all his servants to their current state.
Most are content to play out their lives in the ongoing struggles of law vs. chaos, good vs. evil. Some look to larger prizes, to rise to the ranks of Celestials or even to Godhood.
But a few, a precious few realize that all of existence, all this struggling, is futile so long as the Lady of Pain stands above creation, watching it dance for her amusement. All the suffering of a billion trillion worlds exists because that's how she likes it. They seek some way to escape, to strike her down, to crack open the Cage and be FREE.
The world is a gamble against fate, and the dealer always wins. Unless you find some way to take over the casino or at least escape it. If there is a way, then bold adventurers will be the ones to find it.
Or perhaps die in the attempt.
But it's better than living and dying as rats in a cage, right?
Adventuring in this Cosmology:
Every world determines its nature by the actions of its inhabitants. Every good deed PCs do in the mortal plane of their origin moves it away from the hells and towards the heavens, making life better. Or they might move it towards law or chaos, etc, etc. In other words, the PCs can have a strong impact on the cosmology. Further, unlike standard Planescape where those travelling the planes consider the primes largely home to lackwits, mortal planes may well take on great importance and certainly be worth championing.
One can easily run straight prime plane adventures where it is mainly religion which is affected, planar adventures of the struggle of good and evil and law and chaos or even campaigns with the ultimate goal of breaking the Cage and overthrowing the rule of the Lady of Sigil, so that creation might finally be free to write its own ending instead of dancing for her amusement.
Everything else is give or take, one setting Astral Sea exists the next Mechanus exists, etc.
