A vertical chimney running up through the middle of the pinnacle, entered deep and exited shallow, with light coming down the…A vertical chimney running up through the middle of the pinnacle, entered deep and exited shallow, with light coming down the shaft. Outside, the rock is wrapped in barracuda, batfish and huge schools of chevron and yellowtail, and whale sharks turn up on the seasons. Hin Bai is the best-known dive site in the Gulf of Thailand and the one Koh Tao dive schools save for their students' last day. The Gulf's shallow, warm, enclosed water makes it a nursery, which is why the fish schools here are so dense. Anchorage: No anchorage, but an obvious stop on a Samui-to-Tao passage. Hazards: The chimney is an overhead swim-through with a narrow exit; go with someone who knows it. Plus