The 5-island Surin Archipelago may not be as popular as the Similan Islands to the south, but don't let that fool you into thinking the diving is any less spectacular. In fact, their relative isolation is one of the islands' best traits. Beautiful turquoise water and vibrant reefs offer world-class underwater experiences for divers and snorkelers, while on land native tribes and an unobtrusive infrastructure of basic tents and bungalows allow visitors the rare opportunity to appreciate Thailand at its most unexploited.
Still not satisfied? Then you may want to check out Richelieu Rock 18 km to the east. This lone horseshoe-shaped reef, discovered for diving purposes by Jacques Cousteau, is generally considered to be one of the top 10 dive sites in the entire world. Here you'll find myriad species of fish and marine life, ranging in size from shrimp to the commonly-sighted manta rays and whale sharks that frequent this part of the Andaman Sea. If this hasn't seriously piqued your curiosity, you may be planning a trip to the wrong country.
Note:Because the Surin National Park is somewhat out of the way by conventional standards, adding this to your itinerary will usually require a substantial amount of both money and time. However, for the return on investment, it's awfully hard to say no.