Koh Similan was rated as one of the world’s best spots for both above-water and underwater beauty, the eleven islands at the heart of the Mu Ko Similan National Park are among the most exciting diving destinations in Thailand. Massive granite boulders set magnificently against turquoise waters give the islands their distinctive character, but it’s the 30m visibility that draws the divers. The 5000-year-old reefs are said to be the oldest in Thailand