The Similan Islands: Thailand's Granite Cathedral Reefs
Eleven uninhabited islands in the Andaman Sea where granite boulders the size of houses meet some of Asia's clearest water and richest pelagic action.
Closed for half the year and protected as a national park, the Similans are Thailand's diving crown jewel: dramatic underwater topography, 30 m visibility and a real chance of manta rays and whale sharks between November and April.
Underwater architecture
The west sides of the islands are stacked with house-sized granite boulders that form swim-throughs, arches and sand-floored amphitheatres. The east sides drop into gentler hard-coral gardens — perfect for second dives and check-outs.
Signature sites include Elephant Head Rock, West of Eden, Christmas Point and the legendary North Point — each best dived as a drift on the right tide.
What you will see
Schooling barracuda, big-eye trevally, Napoleon wrasse, leopard sharks resting on the sand, and seasonal mantas at Koh Bon and whale sharks at Koh Tachai. Macro is surprisingly rich on the eastern reefs: ghost pipefish, harlequin shrimp, frogfish.
How to dive them
Almost all serious diving in the Similans is done by liveaboard from Khao Lak — typically 4-day / 4-night trips combining the Similans with Koh Bon, Koh Tachai and Richelieu Rock. Day trips exist but lose two of the four daily dives to transit.
- Best season: February–April
- Departure port: Khao Lak (1.5 h north of Phuket)
- Recommended level: Advanced Open Water + 30 dives
- Average visibility: 20–30 m
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Create my dive tripFrequently asked questions
Can beginners dive the Similans?+
Yes for the eastern sites, but the famous western boulder dives involve current and depth — Advanced certification is strongly recommended.
Liveaboard or day trip?+
Liveaboard, without hesitation. The far northern sites (Koh Tachai, Richelieu Rock) are unreachable on a day trip.
