Just 52 miles northwest of the deckchairs and the bustling crowds of Phuket Patong Beach lies a gateway to another world. Koh Similan is one of the best-known island groups in the Andaman Sea, largely because of the wonders that wait beneath the clear blue waters that surround it. Generally counted among the 10 most interesting dive areas in the world, this little archipelago has also become a favorite destination for yachts and tour boats.

Until the mid-1980s, the Similan were a frontier known mainly to a small number of divers and sailors. "I've dived in a lot of areas that are off the beaten track and... a few where they've never even heard of the beaten track," said Carl Roessler in a 1985 Skindiver article. "Still, my recent adventures in Thailand's Similan Islands have redefined remoteness in dive travel."

But the past dozen years have brought big changes. In the early 1980s, you could spend a whole week out among these islands and encounter no one beyond the occasional long tail boat full of Sea Gypsies. By contrast, in the winter season these days, the best anchorages are a forest of masts, and there's a busy traffic in dive boats and day-tours from Phuket.

What is it that makes these islands so attractive? The Similan aren't as dramatically scenic as the limestone islands of Krabi or Phang Nga Bay which many people have come to associate with the Andaman Sea. Instead, you find low-lying formations covered with thick forest. 

Ironwood and gum trees are among the larger trees, while jackfruit, rattan and bamboo form part of the denser undergrowth. The islands are home to crab-eating monkeys, dusky langurs, squirrels, bats, lizards and a good variety of birds (though the monkeys are shy and rarely seen by the casual observer). But the most striking feature of these islands, at first glance, are the huge boulders that litter the western and southern shores on several of the islands.

Another highlight, as the visitor soon discovers, are the white coral-sand beaches, splendidly picturesque and often deserted. The most interesting sights, however, are to be found beneath the waves. Some of the most spectacular coral growths in the world can be found here - and the same boulders that scatter the shores have turned the waters around the Similan into an adventure playground for divers.