By far, the 'must see' attraction away from the beaches on Samui is the Angthong National Marine Park. This collection of 42 tiny limestone islets 31 km west of Samui sport virgin tropical rain forests, white sand beaches and coral reefs, all preserved as a national park. The park is normally visited as a day trip from Samui, operated by several agencies. The Park Samui reception can help you to book a day trip.

The standard itinerary generally first stops at the park's largest island, Koh Wua Talab, where a steep climb up the island's central peak affords panoramic views as far as the mainland. This climb of about 500 meters is not for the out of shape or faint of heart. There is no stairway, just a cleared seam of limestone that you have to climb. There's a rope to guide you as well as give you something to pull your self up and over some of the bigger stones.

The strong nerves are required towards the end of the climb, where you must scrabble over about ten meters of steep exposed karst to reach the top, where you really are rewarded with a fantastic view.

On the way up or down, you may encounter a troop of spectacled monkeys up in the trees. These are quite an interesting sight, but be careful not to walk directly under them. Their primary defense mechanism when animals get too close is to urinate on them!

Lunch is usually served on board your boat on the way to Koh Mae Koh. Over millions of years, rainwater seeping through the limestone of the island eroded a huge cavern in the centre of the rock. Eventually the roof of the cavern collapsed, leaving a large emerald lagoon completely surrounded by steep cliffs. You reach the lake by climbing a series of ladders up to a deep crevice in the cliff. Squeezing through the crevice and along a walkway brings you to the inner face of the rock wall. From here you can take stairs down to the lake, or up to a viewpoint on top of the cliff. Note that there is no swimming or diving into the lake, but you can see some great wildlife through the clear waters of the lake. The snorkelling off Koh Mae Koh is quite good as well

The cost for the typical tour is 800 to 1,000 Baht, excluding the 200 Baht entry fee to the park.