The Mu Ko Ang Thong National Park is a popular day tour 90 minutes from Koh Samui. Known as the Golden Basin, this archipelago of 42 islands covers 250 square kilometers featuring limestone cliffs, caves, and hidden lagoons. While the movie The Beach was filmed on Phi Phi islands, the original novel by Alex Garland was inspired by the islands of this park.
Most day tours include lunch, sea kayaking, and snorkeling. We booked Samui Island Tour via our hotel, and I can highly recommend them. It was a long day; picked up at hotel 7:30 in the morning, and dropped off 5 p.m. Tired but very happy with the trip.