Have you beaten all monsters in the area? I think there's an area in the upper left that you have to "clear out" too. I'm not sure if destroying crystals will count, but I did anyway. Did Micah/MC say anything about "killing all monsters"? If he did, then there's still an area somewhere you haven't cleared.
^ Yes. But, do NOT use the warp pad. Using it resets the things you killed, so after killing the things on the right side, use the lilypad/ninja shoes to cross the water to kill the stuff at the left side. Then go to the cave and kill the monsters there.
"Think like a man of action, act like a man of thought." -Henri L. Bergson; Join the Dollars @ dollarsgroup.com, pw:baccano