Somewhere off the coast of Phang Nga, granite boulders the size of buildings rise out of water so clear you can count fish from the deck of your boat. That's the Similan Islands, and if the name sounds oddly familiar to Malaysian ears, there's a reason for that too. Here's everything worth knowing before you book a trip out there.

Similan is a Malay word, and it means exactly what you'd guess: nine. The archipelago was originally made up of nine islands, and the name stuck long after the park's boundaries technically expanded to include two more further north.

It's a small detail, but a nice one to know before you go, since almost nobody else standing on that boat deck will realise they're floating over an island chain with a Malay name.

The Similan Islands are only open from around mid-October to mid-May, and for the rest of the year, the entire national park shuts down completely. This isn't a soft recommendation either, the Royal Thai Navy enforces the closure, and boats simply don't run during the off months.

The shutdown exists because the southwest monsoon turns the Andaman Sea rough and unpredictable from May through October, and the park uses that window to let coral and marine life recover from the tourist traffic. So the real question isn't really "when's the best time," it's "which part of the open season should I pick."

December through April delivers the calmest seas, bluest skies, and best underwater visibility of the entire season, with February and March generally considered the sweet spot for diving conditions specifically. This is also, unsurprisingly, when everyone else wants to go, so expect fuller boats and higher prices from December through February especially.

If dodging crowds matters more to you than guaranteed perfect weather, the edges of the season, late October to November, or April into early May, tend to be quieter and noticeably cheaper. The trade-off is a slightly higher chance of choppier water, though it's rarely bad enough to ruin a trip.

Read more: Island Hopping Adventure: 7 Stunning Islands Near Phuket

The Similan Islands are famous for water visibility that regularly hits 20 to 30 metres, which is a big part of why they're consistently ranked among the world's best diving destinations. Underneath the surface, you'll find granite boulder reefs, colourful soft corals, and everything from hawksbill turtles to the occasional manta ray gliding past.

Above the water, the scenery holds up just as well. Sailing Rock on Island 8 gives you a proper hike-to-a-viewpoint moment, and Donald Duck Bay's white sand and oddly shaped boulders have become one of the most photographed spots in the whole archipelago. Since 2018, nobody's allowed to sleep on the islands anymore, so everything here is a day trip or a liveaboard, there's no lounging around after the last speedboat leaves.

Snorkelling at the Similan Islands is genuinely rewarding on its own, since much of the best coral and marine life sits close enough to the surface to see without a tank. Most day trips are built with snorkellers in mind, and you don't need any certification to join one.

Diving opens up a different tier of the experience though, deeper reef walls, better odds of spotting reef sharks, and access to sites a snorkeller simply can't reach. If you're already certified, or willing to squeeze in a quick course beforehand, it's worth the extra cost, particularly during the February to April window when visibility peaks.

Khao Lak is the closer, more practical base, sitting right next to Thap Lamu Pier where most Similan boats depart from. Staying here shaves a couple of hours off your total travel time each day compared to launching from Phuket.

Phuket works too, and makes more sense if you're combining Similan with other stops like Phi Phi or Phang Nga Bay on the same trip. Just be ready for a longer transfer, tours from Phuket typically add an extra hour or two of road and boat time on both ends of the day.

There's no direct route straight to the islands themselves, since they're only reachable by boat from the mainland. The usual path for Malaysian travellers is flying into Phuket, a direct flight of around 1 hour 25 minutes from Kuala Lumpur on AirAsia, Malaysia Airlines, or Batik Air, then arranging onward transport or a tour package to Khao Lak.

Malaysians don't need a visa for this trip either, since Thailand grants visa-free entry for stays of up to 30 days. Just remember to fill out the Thailand Digital Arrival Card online within 72 hours of landing, it's a quick form, but skipping it can slow you down at immigration.

Read more: Phi Phi Island Day Trip Guide from Phuket: Quick and Comprehensive

Since every Similan trip starts with getting to Phuket or Khao Lak, Traveloka, the #1 All-in-one Travel App in SEA*, is a good place to start sorting out the logistics. Your flight and your hotel can both be booked from the same app, so there's less back and forth before your trip even begins.

Flights and hotels on Traveloka come with Best Price Guarantee and 24/7 live agent support. You'll also find access to 2 million plus properties worldwide, flexible pay-later options, and free cancellation on eligible bookings.

You can book flights to Phuket here, browse hotels around Khao Lak and Phuket, and check current Traveloka promos before you lock in your dates.

T&Cs apply. *#1 in cumulative downloads (2014 to 2025) among Travel Booking services apps. Source: SensorTower.