Diving in the Similan Islands in the Andaman Sea, which are among the best and most popular diving areas in Thailand, Kara Murphy discovers that the trick is to find the lesser-known dive sites and shares her discoveries with Boat International.

After being kindly invited aboard the Dunia Baru by owner Mark Robba, my husband, a few other guests, and I embarked on a journey through two countries. We boarded the yacht in Langkawi, Malaysia, and then sailed northwest through the Andaman Sea. We spent a day visiting the Thai islands of Ko Phi Phi Don and Ko Phi Phi Leh, two stunning limestone islands with a particularly beautiful bay that played a starring role in the 2000 adventure film "The Beach."

The Similan Islands (Mu Ko Similan National Park) lie just 60 nautical miles northwest. Their name derives from "sembilan," the Yawi or Malay word for nine. When the park was established in 1982, it comprised nine granite islands, often referred to by numbers: Ko Hu Yong (No. 1), Ko Pa Yang (No. 2), Ko Pa Yan (No. 3), Ko Miang (No. 4), Ko Ha (No. 5), Ko Hok (No. 6), Ko Pa Yu (No. 7), Ko Similan (No. 8), and Ko Ba Ngu (No. 9). Today, the 140-square-kilometer park also includes Ko Bon (No. 10) and Ko Tachai (No. 11) in the north. As one might imagine, their appeal lies in their unique dive sites, which are generally blessed with excellent visibility.

The absolute highlight, Richelieu Rock, lies 40 nautical miles to the north. This remote dive site may not belong to the Similan Islands (but rather to the Mu Ko Surin National Park), but thanks to its diverse marine life, it is considered Thailand's best dive site – one that should not be missed under any circumstances.

We approach at low tide, when the tip of the flat, horseshoe-shaped limestone rock protrudes about a meter above the water. Dreamlike corals in vibrant pink, steaming red, and royal purple shimmer in the beam of my dive lights, providing a gentle refuge for butterflyfish, a hawksbill turtle emerging from the water, pufferfish with eyes the size of ping-pong balls, clownfish, octopuses, and two groupers, while shy scorpionfish—a constant reminder to look but not touch—hide among the colors.

Best time to visit: The Similan Islands are open to visitors every year from November to mid-May; outside of this period they are closed due to frequent storms, strong winds, and high waves. The best visibility is from December to March.

Charter: The Richeliu Rock Dunia Baru can include the Similan Islands in charter trips to or from the Mergui Archipelago in Myanmar. It offers sleeping accommodations for 14 people in one master cabin and six guest cabins.