Richelieu Rock is a dive site in Thailand in the Andaman Sea about 200 km northwest of Phuket. It is part of the Mu Koh Surin marine park although being about 18 km east of Surin Island.
The horseshoe-shaped reef discovered by Jacques-Yves Cousteau is known for its purple corals as well as diverse marine life ranging from small fish and harlequin shrimp to large pelagics like whale shark, manta ray, barracuda, and grouper.
Wikipedia https://en.wikipedia.org/wiki/Richelieu_Rock
Official Website http://www.richelieu-rock.com/
Coordinates 9°21'48.128" N 98°1'15.676" E