When you reach the cave you notice this message stuck to the wall:
Lucky for you I managed to track down one of the natives who gave me these tree clues as to what you are now to do.
The first was this photo:
Se second was to mark the following route on the map:
And the third was a message. "Sacred Llamas love eating hay."
With those clues in mind, I suggest you do what the riddle asks and make your way to the coast where the native marked the X. Once that part of the quest is complete, and you have secured the treasure, you can sail up the coast and return to the ship..
Good Luck Mateys, I'll catch up with you when you reach the coast with your delivery for the natives!
You have till Friday to complete the quest.