Where could the treasure be?

Last October, among all the initiatives, there was a pirate-themed one started by my good friend @guzoborboa (#arghtober). But since I'm a bit of a perfectionist, it took me a while to finish the piece, and the month ended. But here's my idea. I'll probably be able to do it eventually, but first in ink, and then in color. The final image has some digital correction; if you compare them, you'll see the differences.