Dive Sites in Similan Islands (Andaman Sea), Thailand

Richelieu Rock is the reason most people book a Similan liveaboard. This horseshoe-shaped limestone pinnacle, covered in purple soft corals and surrounded by open ocean, consistently ranks among the best dive sites in Asia. Whale sharks pass through from February to April. Seahorses hide in the coral growth. Schools of barracuda and trevally circle the rock in such density that the blue water behind them disappears. On a good day, it's as good as diving gets in Thailand.

The Similan Islands themselves, a chain of nine granite islands in the Andaman Sea, offer a different character. Huge underwater boulders create swim-throughs, archways, and channels at sites like Elephant Head Rock and Christmas Point. East-side sites tend to be gentler, with sloping coral gardens and sandy patches. West-side sites bring the dramatic topography and bigger fish. The granite formations are unique to this area and look nothing like the limestone reefs found elsewhere in Thailand.

Koh Bon, north of the main Similan chain, adds manta rays to the mix. The ridge here is a reliable cleaning station from February onwards. Koh Tachai (currently closed to land visitors but diveable) has a pinnacle that attracts everything from leopard sharks to oceanic mantas. The full liveaboard circuit typically covers the Similans, Koh Bon, Koh Tachai, and Richelieu Rock over 4 to 6 nights.

All of this operates on a strict seasonal window. The Similan Islands National Park opens in mid-October and closes in mid-May. Liveaboards depart from Khao Lak or Tab Lamu pier, about an hour north of Phuket airport. Expect to pay $150 to $300 per night depending on the boat, with budget operators at the lower end and premium vessels pushing higher. Visibility averages 20 to 30 metres, water temperatures sit at 27 to 29°C, and currents range from gentle to moderate at most sites. Richelieu Rock and Koh Bon can produce stronger flow; Advanced certification is recommended for the full circuit.