Koh Tao

Diving here runs on a timetable. Centres send shared boats out of Mae Haad and the southern bays in waves through the day, most trips built around one or two dives with a return to shore in between, and the runs to the nearer sites are short enough that a morning trip is back before lunch. Night dives go out most evenings. Fitting three or four dives into a day takes no special arrangement, and when the boats are full there are bays you can walk or paddle into instead.

The underwater landscape is granite rather than coral rock. The bays are edged with boulder piles running out into sand, which is why the shallow sites are simple to navigate and hard to get lost on, and the offshore pinnacles are the same stone rising from open sand well away from the island. That is where the depth, the bigger schools and most of the current sit. A decommissioned Thai navy vessel sunk off the south of the island as an artificial reef adds the main piece of metal to an otherwise natural set of sites, in around thirty metres, so most centres treat it as an Advanced dive.

The volume of training is the defining fact about the place. Courses start most days, prices stay low, and the ladder runs from first breaths through instructor and technical training alongside an established freediving scene. The flip side is traffic: on a busy morning the popular pinnacles can hold several boatloads at once, so the practical difference between centres is group size, boat load and departure time rather than which sites they visit.

It suits people who are learning, who want to dive a lot cheaply, or who are staying weeks rather than days, and mild current and short crossings to most sites keep it undemanding, though Sail Rock is a longer run out towards Koh Phangan. There is no closed season; October and November are the least reliable months, when rain and surface chop cut visibility and can cancel ferries. Divers set on walls, drop-offs or dependable big-animal encounters will do better on the Andaman side of the country.