Ang Thong National Marine Park is a two hour ferry ride from Koh Samui. I joined a day long tour through the park. We stopped at two islands, Koh Wua Tha Lap, and Koh Mae Koh. At each island, the ferry anchored a couple of hundred metres from the shore, and we were transferred to long tail boats that took us to the beach.

Koh Wua Tha Lap is the largest island in the park. There's a walking trail you can take up the mountain to a lookout from which you can see all of the islands in the park. The trail isn't so much a path as a bit of the mountain that the trees and undergrowth have been scraped off, with rope tied to trees at about waist height. Some sections of the trail are fairly flat, but in others, you have to haul yourself up the rope by your arms as much as by your legs.

The summit is about an hour and a half's hike. The view is pretty awesome. I was wrecked by the time I got up to the top because I forgot to get a bottle of water to take with me, and I was starting to suffer heat stroke. When I got back down I drank two litres of water and went swimming for half an hour.

The main feature of Koh Mae Koh is it's "talay nai" which literally translates to "sea inside". It turns out that this island is a limestone ring around a 4 square kilometre lake that is connected to the sea outside by subterranean canals. The lake is full of all kinds of different fish. Big ones, small ones, stripy ones, ones with long noses, ones with long tails. They seem to gather around the places where the water enters the lake where they can catch bits of food as it floats in.

There is a series of steps (that are so steep they are almost ladders) and catwalks that take you from the beach up and through the limestone wall to the lake. Then from there there's another series that take you up to a lookout on the top of the limestone wall. On one side of the lookout you have the talay nai, and on the other, the Gulf of Thailand.