Located about 90km west of Phuket in the Andaman Sea, a tiny archipelago of nine islands make up the Similan Islands. Travel is only permitted during non-typhoon season, from November-May, since the only way out to the islands is about an hour ride on speedboat. Not all the islands are accessible anymore, as many have recently been closed to the public by the Thai government as sanctuaries for sea turtles.
The islands that are accessible are incredible, with white sand beaches and crystal blue waters. The largest, main island offers tents, bungalows, and a restroom facility, for travelers to spend the night. Some folks can be seen lounging on the beach during the day, but the main highlight to explore in Similan are the waters.
The only way to book is with travel companies on the main island of Phuket, but it's nice because the companies offer all-inclusive overnight packages, complete with snorkeling and diving trips that you shouldn't miss.