A dive site in the Andaman Sea near the Surin Islands, north of the Similan Island Archipelago. It is part of the Surin National Marine Park although being about 18 km east of Surin Island. The most famous dive site of Thailand, Richelieu Rock is an isolated diving pinnacle which is home to the largest and most diverse species of marine life unlike anywhere in the country. The site is marked by the top with a pinnacle which is 1 metre above the sea level during low tide, and disappears underwater during high tide.
The horseshoe-shaped reef discovered by Jacques-Yves Cousteau on his way to the Similan Islands is known for its purple corals (it reminded Jacques Cousteau of Cardinal Richelieu´s purple robe apparently) as well as diverse marine life ranging from small fish to super large pelagics like whale shark, manta ray, barracuda and grouper. The pinnacle falls steeply to the surrounding sand bottom at a maximum depth of 35 metres. The south side is a bay with a slope that gently falls to the deep, while the rest comprises sheer walls, groups of rocks and numerous small caves that are home to various marine life.