Kamikaze Midget said:
Pehraps something to thin of is what kind of material-plane creatures would wind up here, imprisoned themselves? hmmm.m.....
In this vein, you could think Mos Eisley meets Pitch Black (and Chronicles of Riddick [the first bit, not the last bit]), but far, far worse, diverse, and more self-serving. The entire first couple of sessions could literally be comprised of a race for survival on the parts of the PC's - while they are bad in their own rights, they've just been dropped into a pond of horrible, life-long murderers, rapists, madmen, serial killers, etc - all who are raring to slake their blood-thirsts.
There might be paragon werewolves and vampires imprisoned there, render barbarian-murderers, shifter hunter-killers, changling assassins and blackguards, tiefling thieves and backstabbers - the list goes on and on....
Perhaps the party flees the prison into the desolate wastelands of Carceri - the bloodswamps, the skeletal remains of blasted Blood War battlefields, or razor-sharp obsidian mountains filled with renegade fiendish bladelings....
I'd better stop, before I'm responsible for a TPK.

What level are the characters again?
