The Similan Islands are an archipelago of eleven granite islands in the outer Andaman Sea, about 70 kilometres off Thailand’s west coast — and they are routinely ranked among the best diving and snorkelling destinations on the planet. Think house-sized granite boulders stacked into headlands, white-sand bays like Donald Duck Bay, and visibility that can stretch past twenty metres over coral gardens patrolled by turtles, rays and reef sharks. The catch is access: the islands are a protected national park, open only from 15 October to mid-May each year, and getting there takes real planning. This guide covers what makes them special, how to visit sensibly, and an honest word on the day-trip options.
What makes the Similans special
Two things, really. Above the waterline: the granite. Unlike the limestone karsts of Phang Nga Bay, the Similans are weathered granite — enormous smooth boulders piled along the coastlines, with viewpoints like the famous Sail Rock lookout giving postcard views over turquoise bays. Below the waterline: some of Thailand’s richest marine life. East-side dive sites offer gentle coral slopes for beginners; the west side serves up dramatic boulder swim-throughs and current-swept pinnacles for experienced divers. Snorkellers are far from short-changed — several bays offer superb reef access straight off the beach or boat. If snorkelling is your main event, our Phuket snorkelling guide puts the region’s options side by side.
When to go
The park is open from 15 October to mid-May and closed for the five monsoon months — the full rhythm, and the reasons behind it, are in our Similan opening and closing dates guide. Within the open season, November to April brings the calmest seas and the best visibility; the weeks just after the October reopening are the quietest, with the reefs at their freshest after five months without visitors.
How to get there — and an honest word about day trips from Phuket
The Similans are boat-access only. The sensible departure point is Khao Lak on the mainland — about 60–90 minutes offshore by speedboat, roughly an hour’s drive north of Phuket airport. Day trips also sell heavily out of Phuket itself, and here we owe you honesty rather than a sales pitch: Simba Sea Trips does not operate Similan day tours from Phuket, by deliberate choice. We have been running boats out of Phuket since 2005, and twenty years of operating in these waters has settled the question for us: the Similans are simply too far offshore for a responsible single-day speedboat round trip. If a boat loses an engine out there, the limp home takes five or six hours and puts guests back after dark in worsening seas — a risk we are not prepared to price into a day ticket.
So our recommendation is the one we give our own guests: if the Similans are non-negotiable, drive up to Khao Lak and go from there — knowing most Khao Lak operators run big 30-plus-passenger boats, a different experience from a small group. Better still for many travellers: a liveaboard, which is how divers see the Similans at their absolute best, without the daily crossing at all.
The islands themselves
The park comprises eleven islands strung north to south, traditionally known by number as well as name. Koh Similan (island eight) is the largest, home to Donald Duck Bay and the Sail Rock viewpoint scramble; Koh Miang (island four) hosts the park headquarters and two pretty crossing beaches. Several of the smaller islands and their surrounding reefs are protected as dive-and-snorkel-only sites with no landings — part of how the park keeps its recovery ahead of its popularity. Landing rules vary island to island and season to season, so treat any specific itinerary as subject to the park's current arrangements.
Staying overnight
Facilities inside the park are deliberately minimal and park-controlled, and the rules on overnight stays have tightened over the years — most visitors now experience the Similans on a day trip or a liveaboard. If sleeping in the park matters to you, check the current Department of National Parks arrangements for the season you are travelling rather than relying on older articles; capacity is limited and changes year to year.
If the Similans don’t fit your trip
Five months of the year they are simply shut, and even in season the logistics rule them out for many Phuket-based itineraries. The good news: the qualities people chase up there — clear water, dramatic rock, rich snorkelling, small crowds if you time it right — exist an hour from Phuket. Our early-departure Phi Phi Sunrise tour (฿5,310 per person, all-inclusive, maximum 18 adults) reaches the islands before the day-tripper fleet, and a private Phang Nga Bay sunset charter trades coral for limestone karsts at golden hour. The Similan Islands destination page has the full picture of how the archipelago fits the region.
