The Batong Group of islands is as far south as you go on the west coast of Thailand before hitting Malaysia. Here, the towering rock formations and crystal waters of Ko Tarutao National Marine Park, a 61-island group about 30km from the mainland, are still off the radar for tour groups. (These are the only foreign-flagged vessels allowed to work in Thailand’s national park waters.) I learn that the celebrated 1973 movie Papillon, starring Dustin Hoffman and Steve McQueen, was shot here.