This comprises some 40 islands about 20 kilometres or two hours by boat northwest of Ko Samui. The park covers 250 square kilometres, of which approximately one fifth is land mass. The most attractive islands include Ko Wua Ta Lap, Ko Mae Ko, Ko Prayat, Ko Sam Sao, Ko Nai Put and Ko Wua Te. Most islands comprise limestone masses reaching heights of up to 400 metres, and fringed by beaches and rain forest. An emerald saltwater lake known as Tha-le Nai (Inland Sea) on Ko Mae Ko is the parks major scenic attraction, and entails a mildly strenuous climb. The resultant views are well worth the effort. Another popular venue is Ko Sam Sao where an extensive span of coral reef and a huge rock arch offer scenic fascination. The park office is on Ko Wua Ta Lap