KO MOOK, about 8km southeast of Ko Hai, supports a comparatively busy fishing village on its eastern side, around which – apart from the sandbar that runs out to the very pricey Sivalai Resort – most of the beaches are disappointing, reduced to dirty mud flats when the tide goes out. However, across on the island’s west coast lies beautiful Hat Farang, with gently shelving white sand, crystal-clear water that’s good for swimming and snorkelling, and gorgeous sunsets.

Tham Morakhot

The island’s main source of renown is Tham Morakhot, the stunning “Emerald Cave” north of Hat Farang on the west coast, which can only be visited by boat, but shouldn’t be missed. An 80m swim through the cave – 10m or so of which is in pitch darkness – brings you to a hong with an inland beach of powdery sand open to the sky, at the base of a spectacular natural chimney whose walls are coated with dripping vegetation. Chartering your own longtail or taking a trip with Ko Mook Nature Beach Resort (B200/person, in a group of four or more) is preferable to taking one of the big day-trip boats that originate on Lanta or Pak Meng: if you time it right, you’ll get the inland beach all to yourself, an experience not to be forgotten. It’s also easy enough to kayak there from Hat Farang (from B100/hr from Sawaddee), and at low tide you can paddle right through to the inland beach: buoys mark the cave entrance, from where a tunnel heads straight back into the rock; about halfway along, there’s a small, right-hand kink in the tunnel which will plunge you briefly into darkness, but you should soon be able to see light ahead from the hong. Mid-afternoon is often a good time to paddle off on this trip, after the tour boats have left and providing the tide is right.