D'oh!
Thanks for that tip, sir. I assumed the cave-ins weren't selectable, or were made out of the same material Ornate Chests are, thus making them invulnerable.
Also, I agree about the White Witch quest not directing you terribly well. I wound up doing tons of higher-level stuff before I wound up getting annoyed and retracing my steps.
For everyone looking for a cave to find the barrier scroll, spoilers:
STOP looking for a cave. The scroll can be found on the heavily trapped hill right next to the drunk goblin area. It's in a hidden, buried chest at the top.
