Boulder City, Similan Islands - Thailand Dive Sites

A dramatic deep water Similan dive site, Boulder City needs the right conditions to explore as it’s exposed to wind and wave from all sides

Pook and the big boulder, Boulder City, Similan Islands, Thailand, December 2024 © chris@divehappy.com

I’ve only dived Boulder City a handful of times as it doesn’t come up that often on standard Similan liveabaord itineraries. Reason being Boulder City doesn’t sit off one of the Similan Islands themselves but out in the deep water channel about a kilometre from Similan island number 3.

Fusiliers and fan corals on the rocks, Boulder City, Similan Islands, Thailand, December 2024 © chris@divehappy.com

That means it’s a deeper dive – the highest point in the site is about 18 metres – and because there’s no island to provide cover, the tides and currents need to be cooperating to safely get on and off the site without being blown off into the blue.

Pook and snapper over big corals, Boulder City, Similan Islands, Thailand, December 2024 © chris@divehappy.com

The upside is that you’re usually the only divers on the site so it’s worth the effort. Boulder City is a dramatic collection of huge rocks rising up out of the white sand with a lot of large fan corals and big schools of fusiliers running between them. The site has a real crackle of electricity to it. Being deeper and quieter means there’s also the sense that something big might pass by at any moment.

Fusiliers clustering over the rocks, Boulder City, Similan Islands, Thailand, December 2024 © chris@divehappy.com

Boulder City is located not far from Shark’s Fin Reef, another deep big rock Similan site out in the channel. It’s theoretically possible to swim from one site to the other but unless the current and visibility is on your side, probably not recommended.