Similan Islands

The Similans break Thailand's limestone habit: this Andaman archipelago is granite, its islands stacked with smooth house-sized boulders that continue underwater into swim-through dive terrain rated among the world's finest. Mu Ko Similan National Park protects eleven islands of blinding sand and glass-clear water - visibility runs to tens of metres in season - with the Sail Rock boulder above Donald Duck Bay serving the postcard climb. Divers come for soft-coral walls, rays and the season's chance of whale sharks; snorkellers get their share straight off the beaches. The park closes annually from mid-May to mid-October while the monsoon scours the sea lanes, reopening each October to speedboat day trips from Khao Lak and to the liveaboards that do the islands fuller justice. Daily visitor caps and recovery closures - Ko Tachai among them - guard what makes it worth the ride.

What you actually see

• Sail Rock viewpoint - the boulder climb above Donald Duck Bay.
• The dive reefs - granite swim-throughs, rays and seasonal whale sharks.
• The white-sand beaches - blinding crescents against clear turquoise.
• The snorkel bays - reef fish in glass-clear shallows off the sand.

When to go

Open only 15 October to 15 May; February to April brings the calmest seas and best visibility. Book ahead - high-season day trips and liveaboard berths sell out.

Honest expectations

Speedboat rides are long, fast and hard on weak stomachs. Day-trippers share the same few bays at the same hours - liveaboards escape the rhythm. Visitor caps, no-plastic rules and closed islands are enforced, and rightly.

Nearby

Khao Lak's mainland beaches, the Surin Islands and Phang Nga province.