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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
Pook and the big boulder, Boulder City, Similan Islands, Thailand, December 2024 © [email protected]

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
Fusiliers and fan corals on the rocks, Boulder City, Similan Islands, Thailand, December 2024 © [email protected]

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
Pook and snapper over big corals, Boulder City, Similan Islands, Thailand, December 2024 © [email protected]

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
Fusiliers clustering over the rocks, Boulder City, Similan Islands, Thailand, December 2024 © [email protected]

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.

Recommended Similan Liveaboards October 2025 to May 2026

Blue Dolphin Liveaboard

Blue Dolphin Liveaboard A mid-range liveaboard with 7 cabins for 16 people. Check availability and pricing

The Phinisi Liveaboard

The Phinisi Liveaboard A Similan mid-range liveaboard with 7 cabins for 18 people.Check availability and pricing

Smiling Seahorse Liveaboard

Smiling Seahorse Liveaboard A mid-range liveaboard with 8 cabins for 16 people. Check availability and pricing

The Junk Liveaboard

The Junk Liveaboard A mid-range liveaboard with 6 cabins for 18 people. Check availability and pricing
 

2026 Thailand Last Minute Liveaboard Deals

Similan Islands Dive Sites List

Similan Liveaboards Overview

Upcoming Similan Liveaboard Availability and Pricing

Check availability and pricing for all Similan Islands liveaboards departing in

(The Similan National Park is closed from mid May to mid October each year)

Similan Liveaboards Trip Reports

Photos from each of the Similan liveaboard trips I've been on over the years.

Similan Dive Sites

Richelieu Rock

Soft corals at Richelieu Rock, Thailand Thailand’s best dive site, bar none. A stunning array of soft corals and spectacular stampeding marine life. Read More

Koh Bon

Manta Ray at Koh Bon ridge, Thailand Thailand’s manta ray hotspot, with plenty of other things to see if the mantas don’t show up. Read More

Koh Tachai

Barracuda ball at Koh Tachai, Similan Islands Koh Tachai is one of the Similan Islands’ best dive sites but also one of the most volatile. Massive fans, huge schools of fish, maybe manta rays – it’s all to play for. Read More

Boulder City

Diver with boulder and fan corals, Boulder City, Similan Islands 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. Read More

Shark’s Fin Reef

Big boulder split in half, Shark’s Fin Reef, Similan Islands A dramatic block of rock rising out of the sand, Shark’s Fin Reef is one of the Similan Islands’ most exciting sites. Read More

Hideaway Bay

The Tuna Wreck, Similan Islands Two Similan Islands dive sites in one location, Hideaway Bay and Tuna Wreck can be experienced in a single dive. Read More

North Point

Fan corals on big boulders at North Point North Point is another of the Similans’ signature big boulder sites, with huge great rocks rising out of the white sand. Read More

Koh Bon Pinnacle

Yellow corals at Koh Bon Pinnacle Koh Bon Pinnacle is a deep dive site that feels utterly remote – and where anything could show up out of the blue. Read More

West Of Eden

Giant fan corals, West Of Eden, Similan Islands A big boulder site with spectacular outsize fan corals, beautiful soft corals and the promise of full fish activity, West Of Eden is an archetypal Similan Islands dive site. Read More

Ao Suthep, Surin Islands

Hard coral garden, Ao Suthep, Surin Islands Ao Suthep is beautiful hard coral garden in the Surin Islands, often visited by Similan island diving liveaboards and accessible by snorkellers visiting the Surin Islands too. Read More

Three Trees

Giant barrel sponge, Three Trees Three Trees, named after the three trees directly above the dive site on Similan Island 9, is a big wide white sand channel with some awesome corals and fish encounters. Read More

Christmas Point

Fan corals and curved rocks, Christmas Point One of the signature Similan Islands big boulder dive sites, Christmas Point’s huge rocks have been shaped by the tides over hundreds of years. Read More


Diving And Travel Insurance

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Start Planning Your Thailand Dive Trip Now!

:: Check the availability and pricing of liveaboards in Thailand and book online.


:: Find the cheapest flights to Thailand - Phuket (airport code: HKT) is the nearest airport for diving the Similan Islands. You can get direct international flights to Phuket or go via one of Bangkok's two airports - Suvarnabhumi (BKK), the main airport, or Don Mueang (DMK), the low cost carrier terminal.


:: Make sure you don't forget to bring any of the essentials for your scuba diving trip with our comprehensive Liveaboard Packing List


:: World Nomads offers simple and flexible travel insurance. Buy at home or while traveling and claim online from anywhere in the world.


:: Find available places to stay in Phuket for before and after your liveaboard on Booking.com - usually you can reserve a room with no upfront payment. Pay when you check out. Free cancellations too.


:: Need inspiration? See our Best Places To Dive In Thailand for ideas of where to go and what to do.


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