differentiating the prisons

Pitiless.

Pitiless = "blast from the past" for DMs. You can stash any old NPC from like, 8,000 years ago in here if you want. Someone also might end up in Pitiless if they have a powerful enemy who, for whatever reason, doesn't actually want to kill them. Killing an uber-good paladin, for example, would only send his spirit to a happy Upper Plane, but if you send him to Pitiless, he'll be uncomfortable for a very long time.

The 'theme' of Pitiless is timelessness/decay. Anything in the Astral Plane is immune to the natural processes of time, but the Sinkers run the place.

We're also forgetting those very personal prisons, The Mazes.

Jareddm, my PCs may be stepping into Archeron for the first time ever next session, nice idea. Bwa hahha!!

Do you have a link for that? 

That I do good sir.

http://forums.gleemax.com/archive/index.php/t-1020533.html 

odd...works just fine for me.  Takes me right to the wizards archives.

Anyone else having this problem? 

Now it works for me, too.

"Keeps your ears turned this way, Bubber, I heard it best from a kiddie in Plague-Mort.  Little Girl, no bigger than one of me legs, she tells me: Everything after here is a prison.  Damned if she weren't correct too." - Kalo Brandmark, Tiefling Guardian factioneer

 The truth of the lower planes (not the fact) is that they are all prisons of one sort or another.  Certainly, in the case of pandemonium or Carceri, some planes wear it plainly.  Others are far more insidious.  In general, the chaotic planes represent the self imprisoned and beset by outside forces, while the lawful planes represent the self buried by the collective.

Pandemonium's prison status is sometimes entirely obvious: Agathion is the place where great beings hide forever those that could destroy the multiverse.  For the most part, though, people imprison themselves in Pandemonium, attempting to escape all others.  It would be the perfect place to get away, too, what with it being dark, desolate, cramped, little more than a series of holes burrowing through the infinite earth.  Perfect, that is, if not for the howling winds, cursed winds that carry with them the voices of everyone the subject has ever wronged, everything they've lost.  The madness of the plane isn't created by the wind, it's created by the individual until they are imprisoned within their own skull, unable to make anyone else understand the curse they suffer from.

The Abyss's prison is one of desire:  if one is capable, the plane can give any being anything they've ever wanted.  But it's never perfect.  And even when that objective is met, the beings look to further conquests.  All Abyssals are forever imprisoned as they will never learn that every victory will feel hollow. Ultimately, satisfaction is an impossibility.  

Carceri is another obvious prison: between the Ghereleths,  the Titans, and the other overthrown progenitors of the planes, Carceri is full of those who have been conquered and imprisoned.   Carceri's prison status is one of beings who have been punished for horrible actions.  Release is an impossiblity, too, since the inhabitants commit betrayals and crimes that only prolong their stay.  The only means of leaving is true repentance... but that has yet to happen.

The Gray Wastes imprison the being within itself, a sensory deprivation of the grandest scale.  On Oinos, the senses are assaulted by the war and disease: hearing is corrupted by the moans of the stricken and the clash of the battles; the visuals of dead and dying are everywhere, with atrocities committed beyond comprehension; olfactory fatigue sets in after experiencing the ever present scent of charred flesh, dead bodies, and offal; even taste  is assaulted, as what is smelt is often experienced by the tongue.  Niflheim's winter numbs the body, but beyond that emotions slowly drain out in this climate.  No longer does one feel the heat of rage, instead they are left with cold clarity and cold blades, because numb hands don't feel the heat of blood.  Finally, Pluton, the realm of Hades is where one loses faith.  In a realm where one can directly experience the result of hubris, the mortals sentenced to relentless torture become pitiable, and eventually one cannot look upon the other gods without seeing the crimes they commit upon those much weaker than them.  No longer can a body experience the soaring of belief after a stay in Pluton.

 Contrary to popular belief, Gehenna is one of the loneliest planes.  In a plane where willpower is the metric of power, there are only two beings:  I, and the others.  The solo being subjugates those beneath him by bending them to his will, perhaps through threats or intimidation, perhaps by proving himself capable of committing acts for no reason other than to prove a point.  The subjugated beings are imprisoned by will, the one who pulls the strings is imprisoned by his own will, never able to see others as peers or equals: in Gehenna, they are all potential subjects.

Baator is also a prison where the individual is subjugated, but not by individuals: instead by the Devils themselves, the Baatezu.  This is the imprisonment of the self by the party.  Rah rah rah!  Eventually one won't even realized they are in prison, until they mess up.  Then, like all Infernal bargains, one realizes they mired themselves in a situation they can't even comprehend.

Finally, Acheron: the plane where warriors go to lose joy in battle.  Acheron is all about post-traumatic stress warriors, those who keep the battle raging long after it is over.  Look at the Rakshasa, attempting to assert themselves against the Vedics despite the knowledge that the war was won a very long time ago, and that the Rakshasa are now little more than flies.  And yet, the war has gone on for so long, it's now all that they know.  

I always thought that Belieren's staus as a prison for evil critters was a little odd. After all, if there is a horribly evil sentience within Belieren, what would prevent it from slipping out of Elysium and joining the lower planes?

 IIRC, the layer contains some of the primal evil creatures - the first Medusa, first Hydra, etc. This is in addition to the "unnamed evil entity". Again, why should there be an "evil" plane in the layer that is devoted to the highest good? Consider the power of the Gray Waste, which saps emotion even from the Powers themselves. Elysium should be similarly powerful.

Here's my take on Belieren: There are such creatures which exist. However, rather than being evil, they have turned good. However, they know that the effect of the Gray Waste will fade over time if a creature leaves. They are worried that the same may apply to Belieren's effects. So as newly good creatures, they have set themselves into a state of exile until such time as they can leave the layer and be certain they won't slide back into evil.

 The unnamed evil fiendish lord/evil monster may be a redeemed unique Yugoloth or other fiendish lord. He(?) knows that if his redemption is discovered, the forces of evil would stop at nothing to destroy him, causing untold damage to the upper planes. Potentially the forces of the Abyss and Baator might see the possibility of a Lord converting to good as a huge danger, and might pause the Bloodwar to destroy the former Lord.

Thoughts? 

I'd add that Elysium is intended to be just a little creepy with tinges of "good gone too far." Despite what Jem said, the plane does change people, it makes them a little more charitable, a little more good, and it makes them never want to leave. Elysium isn't all sunshine and kittens. It tests you against evil to see how you fare, saps your desire to leave, and eventually subverts your will (and mortality) and turns you into a petitioner. Sure it grants eternal bliss, but at the expense of free will and individuality, which, frankly, kind of sucks. Add to that the fact that Guardinals are by far the creepiest looking Celestials, and a secretive prison plane doesn't seem too out of place anymore.