Boulder City is a cluster of underwater boulders and is located of the southeast coast of Island No.3 next to Shark Fin Reef. Two of the boulders lie at about 12-18 meters below the surface and are covered with soft corals and seafans. Clumps of staghorn coral are also scattered around the boulders.

The marine life here is truly diverse with large Groupers, Snappers, Angelfish, Unicornfish, Boxfish and Pufferfish being commonplace. Pipefish & Fire gobi’s can be seen in the rocky crevasses of the boulders.