Koh Tao — Turtle Island — is a small island in the Gulf of Thailand, about 70 kilometres north of Koh Samui and part of the Chumphon Archipelago. It covers just 21 square kilometres, but its combination of clear warm water, accessible coral reefs, and low cost of living has made it one of the world's most popular destinations for learning to dive. More Open Water PADI certifications are issued here per year than almost anywhere else on earth.
The island has a split personality. Mae Haad on the west coast is where the ferries dock and the budget accommodation and dive shops are concentrated — busy, sociable, and very much a traveller hub. The Sairee Beach strip to the north is the liveliest stretch, lined with bars, restaurants, and dive operators. But a short walk or motorbike ride takes you to the other side of the island, where Tanote Bay, Chalok Ban Kao, and the northern headlands are quieter and wilder.
The reefs around Koh Tao are genuinely good — not pristine, but home to healthy coral, sea turtles, reef sharks, and large shoals of fish. The visibility is often excellent. For non-divers, the snorkelling is impressive at many spots accessible directly from the beach, including at Shark Island and Japanese Gardens.