I just got the Planes of Conflict boxed set (a friend who was going into the military GAVE it to me, only missing the top of the box) and was reading about Carceri and Gehena. These two planes are fairly unique by comparison to all of the other planes.
Gehena is four land masses suspended in an infinite void.
Carceri is a "string of orbs" suspended in a void.
Unlike planes like Archeon and Mechanus, which are similar in this respect, there is "nothing" in this void. No further volcanoes or orbs.
So, let's say you really wanted to imprison some really awful thing, or hide something, or just get rid of something.
You go out, oh, lets say about 700,000 miles into the void and start building a fortress. The chances of anyone who doesn't know about it comming here are ridiculously low (why is anything going to just randomly choose to start heading 700,000 miles into the void where "nothing" exists for them to get to anyway?). You can use it as a prison, a secret base, whatever. Who in the planes is going to find it?
Getting to the area initially would be a pain (how do you propose one goes that far out into the void?). However, once you've been there, getting back woudl be easy with teleportation spells/powers/items.
Has anyone ever played with this idea before? There could be a whole town of REALLY bad prisoners on the sixth layer of Carceri just completely isolated, not even on one of the orbs. I would want to visit that town myself . . . if they were too bad for one of the orbs of the lowest layer no good could come of going there . . .
It's kinda been done by something. Remember the Bells of Carceri? I'm pretty sure that's in Planes of Conflict.
Regardless, it sounds like a good plot hook.