Related to this thread (concerning the use of demiplanes as prison cells/oubliettes) I was wondering about two things.
1) How does flying work in an (antimagic) area without air? Does non-magical flight work without air? (physics says no but this is PF).
2) Can you climb a "mist, a featureless void, or a similar unreal-looking border"?
The context: if you'd create a cylinder-shaped (dead magic) demiplane surrounded by an 'unreal' border, gravity oriented towards one end and a permanent planar portal on the other (basically resulting in a demiplanar pit), could characters climb out?
The “walls” and “ceiling” of the plane may appear like solid earth, stone, wood, or water, or they may end in mist, a featureless void, or a similar unreal-looking border.
PF has no rules for such a situation, so that's purely houserule territory. If you prefer physics, feel free to rule that non-magical flight doesn't work unless it relies on being lighter than air.
As for the climbing thing, it says that the walls and ceiling only appear like things. They're actually just the end of the world if you don't decide to have the plane wrap around. I'm pretty sure you can't climb the edge of the demiplane.