A City in Agathion Pandemonium

The Green Orb is actually a prison for an outsider: Baatezu, Tanar'ri, Obyrith, Yugoloth, Far Realm, take your pick. Somehow, it discovered secrets of mental control beyond any known by any other force, powerful enough to pierce even the most potent magical defenses. The powers quickly realized what a threat this could be to their followers (and, by extension, to their own power) and bound the creature in the orb, sealing it away in Agathion. However, with nothing else in the cave to occupy itself, the creature could focus its considerable intellectual and magical faculties on escape, and given enough time it was bound to succeed. Thus, the powers (not all of them if you prefer, just whoever was involved in this whole incident) each sacrificed a few of their worshipers to populate a city ringing the orb. These mortals live their daily lives not too differently from those of any other planar or prime city, other than the fact that their sole true purpose is to keep the creature in the orb amused. The city allows it to exercise its mental domination at its leisure, keeping it too entertained meddling with the petty lives of those mortals to think too long or too hard about escape.

Of course, as a safeguard against any planewalkers stumbling into the city and giving the creature new information or magical means of freedom, the powers made sure the city had a tendency to eliminate any outsiders that appeared....

I meant to put Ancient Baatorians, sorry, merely forgot. The Draedens I've seen here and there but am less familiar with. Some sort of pre-time tentacle-y things, right?

The city has no children (or very few) because every inhabitant of the city is a would-be tyrant, dictator, warlord, and so on. Various worlds across the Prime, and even a few planar realms, have discovered a ritual allowing them to banish individuals who threaten the peace through war, genocide, and the like. What none (or perhaps merely a few) of these individual groups know is that the ritual always sends them to the same place. However, the Green Orb pacifies the former conquerors, reshaping their personalities as simple bakers, smiths, and tailors. They forget their old lives and live peacefully in the city, not even aware there is a world outside the cave.

Of course, the PCs could need to visit one of these men or women for information their old personality knew. Not only would they have to discover a way into a specific sphere of Agathion, but that they would also have to learn how to unlock the buried memories, avoid the orb's efforts to stop them, and moreover, make sure that the individual they restore does not become a greater threat than whatever they were trying to stop in the first place.