Widely considered Koh Tao's premier dive site, Chumphon Pinnacle is also one of the island's most challenging with occasionally strong currents.
Ranging from depths of 12m to 40m, the site is a group of massive rocks arranged in a rough oval and running north to south.
Visibility is superb in season, and the site plays host to a wide variety of pelagics as well as reef fish. Great barracuda, king mackerel, grouper, and tuna throng to Chumphon all year around, and in season whale shark sightings are common.
As the site is a fair distance offshore, visitors from the open ocean are unpredictable -sailfish, oceanic white tip sharks and bull sharks have also been spotted.
Southwest Pinnacle, a series of rock formations ranging from 4m to 30m and is another of Koh Tao's top ten. The tops of the pinnacles are covered with a carpet of anemones in brilliant greens, pinks and blues, with their cavalcade of pink anemone fish. Leopard sharks and whale sharks are occasional visitors to the site, which is home to large schools of snapper, yellowtail barracuda, as well as fusiliers.
Large groupers can be seen here as well, along with scribbled filefish and masked porcupine fish. The observant diver may spot scorpion fish and stonefish camouflaged on the rocks.
A single rock that protrudes from the water between Koh Tao and Koh Phangan, Big Blue in Koh Tao visits Sail Rock less often than the other sites, but the dive is well worth the trip.
The most noticeable feature of the dive is "the chimney" - a vertical tunnel in the rock that leads you from 18m to 8m, but the entire site (from the surface to 45m) is full of points of interest. The rock is riddled with small holes which makes a perfect habitat for white eyed and yellow margin moray eels, and the large anemones that cover it are filled with anemone fish and shrimp.
Whale sharks can be seen in the winter months here as well, and keep an eye out for other large pelagics. Octopus camouflage themselves so exactly to match the covering of the rock that you may miss them completely, but keep your eyes peeled - they are there.
Possibly Koh Tao's most varied site, Shark Island is a small uninhabited island just to the southeast of Koh Tao. Sloping gently from the surface down to 24m, there is always something new to see here including some of the Gulf of Thailand's most stunning soft coral.
White eyed moray eels, blue spotted fantail rays, porcupine and puffer fish, and an enormous variety of reef fish are almost guaranteed in the beautiful shallow coral garden, while the fortunate may also see whale sharks, leopard sharks, reef sharks and other pelagics on the deeper side.
Titan triggerfish add an element of excitement to each dive, and divers often spot turtles and sea snakes.
Fascinating rock formations create small caves and swim throughs at Green Rock, which ranges in depth from 4m to 28m. Brightly colored nudibranchs are omnipresent, as are morays, harlequin sweet lips and blue ringed angelfish.
White tip reef sharks can be seen from time to time, and at the deeper end of the site large grouper and schools of yellowtail, fusilier and silverfish can be seen. Look out for "the minefield", where scores of yellow margin and Titan triggerfish have made their nests in sandy pits.
Say hello to Trevor! White Rock, consisting of two groups of rock separated by a narrow channel of sand (depths from 9m to 24m), is home to Koh Tao's single most notorious fish: Trevor the Trigger. A Titan triggerfish that has been the boss of the site for years, Trevor occasionally takes exception to divers disturbing his rest.
But no need to spend the dive looking over your shoulder, let Big Blue's instructors and divemasters keep an eye out while you enjoy the sea snake, turtle, moray, blue spotted ray, butterfly fish or angelfish.
Look closely in the stag horn coral for porcupine fish and hermit crabs, and see if you can spot a well-camouflaged scorpion fish or two.
Hin Wong Pinnacle
On the east side of Koh Tao lies Hin Wong, a large and very varied site ranging from depths of 10m to 32m. Although visibility here is unpredictable, Hin Wong is covered in lacy sea fans and curly wire coral, as well as filefish, snapper, coral grouper and other reef fish.
The resident turtle is only shy if you get too close. Observe her from a distance and she'll eat placidly away.
For the macro-minded, Hin Wong also has some beautiful invertebrates. Look especially for brightly colored nudibranchs.
Do you remember when your instructor told you to look for the small things? Twins is the ideal place to take that advice.
Two groups of rocks at depths from 10m to 18m. Your divemaster or instructor may show you the haunts of grouper, panda clownfish and stingrays, but if you take your time and look closely you might also see anemone shrimp, morays, flatworms and pipefish, as well as cleaner wrasse at their never-ending work.
Check the crevices for baby angelfish, keep an eye on the water above for squid and crocodile longtom and look for the dancing fins of the juvenile sweet lips.
Nang Yuan Pinnacle and Cave
Koh Nang Yuan lies northeast off the coast of Koh Tao. Nang Yuan Pinnacle, is a small granite pinnacle that rises out of the water from depths of about 20-24m. This dive site is suitable for all levels though during full moon, currents may be experienced.
Whip coral, soft coral and sea fans are common and blue spotted stingrays are abundant and a huge number of groupers can be seen hiding in nooks and crevices. Turtles are sometimes seen foraging among the coral or resting on top of the pinnacle.