Intermediate Thailand
Similan Islands
Underwater granite boulders in the Andaman, with a season of about seven months
Nine granite islands in the Andaman Sea, their rounded boulders continuing underwater to form arches, caves, and corridors. The park closes for about five months a year, and that's exactly why it's still in such good shape.
In this profile you'll find out why the Similan seabed is granite rather than coral, how the east and west coasts of the islands offer two distinct kinds of diving, when the park opens, what wildlife shows up, and what level each side demands.
It's the benchmark destination for Thai diving in the Andaman and one of the few marine national parks in Southeast Asia that enforces a full, multi-month seasonal closure.
Geography and access
The archipelago is made up of nine main granite islands off Thailand's west coast, within a marine national park.
Geology defines the diving here and sets it apart from almost everywhere else in Southeast Asia: rounded granite boulders stack up underwater to form arches, channels, and wide caves, with soft coral and gorgonians growing on the rock.
The two sides of the islands behave in opposite ways. The east side has a gentle slope, with hard coral gardens, white sand, and calm conditions. The west side is where the granite boulders, the current, and the most demanding dives are.
The park closes completely during the southwest monsoon, roughly from mid-May to mid-October. Outside that window you can't get in, and that restriction is part of why the reef can handle the pressure for the rest of the year.
Access is a domestic flight to Thailand's west coast and boarding a liveaboard or, for the nearer islands, fast day trips.
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