By far the best diving takes place in the area northwest of Phuket Island. This area offers both the expert and beginning diver the opportunity to observe large animals in the wild including exciting silver tips sharks, huge whale sharks, occasional contact with migrating pseudo orcas and dolphins and other pelagic wonders such as manta rays. It is also one of the best areas in Southeast Asia for water clarity and a tremendous growth of pristine corals and kaleidoscopic fish. This triangle includes:

The Similan Islands feature huge granite boulders forming swim-through and overhangs as well as incredible varieties of soft corals in a rainbow of colors. This is the most famous area for diving in Thailand because of the beautiful beaches, water clarity averaging 20-30 meters, and the biggest concentration of small tropical fish. Truly world-class diving.

The Burma Banks, located 180 kilo-meters northwest of the Similans, are a series of underwater mountains rising up from over 350 meters to within 15 meters from the surface. Located in open ocean far from shore, these banks are famous for large animal action, including free-swimming nurse sharks and large silver tip sharks . Some operators offer a controlled shark attraction experience using freshly caught tuna for bait.

The Andaman Islands, part of India, have just opened up after more than 50 years of isolation from the outside world. Located another 400 kilometers from the Banks, these islands are just now being explored by several diving operators out of Phuket. Almost no commercial fishing is allowed in the Andamans, thus the size and numbers of fish are frankly amazing.

The Surin Islands, located right on the border with Burma, are visited mainly for an underwater rock located just to the east named Richelieu, which is one of the best areas of the world to consistently observe the massive whale shark. Lush growths of soft coral cling to the rock while large schools of pelagic fish circle it feeding on the abundance of food found here. Peculiar animals such as the guitar shark, large octopus, and cuttle fish are commonly sighted here as well.

Ko Bon and Ko Tachai are located between the Surins and the Similans and feature vertical walls, large sea fans of every shape and size, rays, and leopard sharks. These islands are normally visited on the way back to the Similans from either the Surins or the Banks.
Most of these areas can only be visited by way of live-aboard dive boats. Trip duration is between three and fourteen days and costs vary depending on the comfort and size of the boat, destination, and of course, length of trip.

Day trips and shorter live-aboard are available from Phuket, Ko Phi Phi, Krabi and Ko Lanta. The highlights are:

Ko Dok Mai features a vertical wall plunging to almost 30 meters. Colorful crinoids adorn the wall and a wide variety of fish patrol the depths.

Shark Point lies about two hours to the east of Phuket and is one of the most popular day trips because of the colorful and prolific marine life found there. It is named after the friendly, approachable leopard shark, which can be observed on most dives. Although visibility varies, this is one of the most beautiful sites in the Andaman Sea.

The Phi Phi Island group is also a popular day trip from Phuket and Krabi, but accommodation and dive centers are available on the island as well. Stunning scenery both above and below the surface of the sea and the tremendous variety of diving environments makes Ko Phi Phi one of the most visited places on the west coast of Thailand.

Ko Ha, about two hours south of Phi Phi, has better visibility than does Phi Phi and divers can enter a large cave and actually surface inside of the island.

The islands of Krabi offer cave diving, a ship wreck or two, and inviting coral gardens visited by dive centers located on Ao Nang and Ao Phra-nang.

Hin Daeng and Hin Muang are two pinnacles located southwest of Ko Phi Phi and visited by live-aboard boats from both Phuket and Phi Phi. Aside from the Similan Islands, these two dive sites feature the finest diving in Thailand. Literally covered in pink and purple soft corals, you 'll find large schools of fish, amazing amounts of anemones, and sharks and rays. Also, along with Richelieu Rock, this is one of the most probable places to sight a whale shark.

The twin islands of Racha Yai and Racha Noi are located directly south of Phuket and are visited by both live-aboard and day-trip boats. Since they lie offshore, the visibility here often exceeds 20 meters. Drift diving over sloping hard coral and granite boulders is the norm.