Talk to the girl in front of the billboard, she'll give you hints as to what you should be doing.
Yeah that was a pain in the ass. I thought I'd be able to get through without Flash but NOPE. Best I can suggest is you try to find the exit and head back to Gearan city. Play some voltorb flip, getting 1000 coins is very easy with that game. Or just buy the coins. Flash makes the cave exploration a lot easier. Fumbling around in the darkness makes the cave seem a lot bigger than it really is.