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The Emerald Cave, Tham Morakot in Thai, is a sea cave on the coast of Koh Mook, an island in neighbouring Trang province south of Koh Lanta. Visitors swim through a dark tunnel and come out in a small enclosed lagoon, a hong, with a tiny sandy beach and cliffs rising on every side. That reveal, from darkness to a green-tinted, roofless chamber, is why it is one of the most photographed spots in the area.
What the visit involves
- 1The swim through the tunnel: the cave is entered from the sea and the tunnel is long and dark. Visitors normally swim in wearing a life jacket, often following a guide with a torch. Only go if you are comfortable in open water and enclosed spaces.
- 2The hidden lagoon: at the end, the tunnel opens into a small lagoon ringed by high limestone walls with a small beach and jungle overhead.
- 3Timing and tides: conditions in the tunnel depend on the tide and sea state, and operators plan around them. Try to arrive when it is not crowded; midday can be busy with boat groups.
- 4Koh Mook: the island is a low-key stop in its own right, with quiet beaches and a few small resorts.
- 5Combine it with other islands: Many multi-island days pair the Emerald Cave with Koh Kradan. Compare the main day-trip options before choosing an itinerary.
How people usually get there from Koh Lanta
The cave is not on Koh Lanta. Most visitors reach it from Koh Lanta as part of a longtail or speedboat island-hopping day, or from Koh Mook itself by chartered boat. Many multi-island tours also stop at Koh Kradan. Itineraries differ from operator to operator, so check that the Emerald Cave is explicitly listed before you book.
Seas are rougher and many boat trips run less often in the rainy season. If the Emerald Cave is a priority, plan your trip for the dry season and confirm conditions with your operator. A national park or landing fee may apply and may or may not be included in a tour price.
Koh Muk and Koh Mook are the same island: the spelling varies between maps, operators and booking sites, so search for both when you compare trips. The visit itself is short, and the swim through the tunnel is the main event. Confident swimmers find it easy, but anyone less at ease in the water should wear the life jacket operators usually provide.
A Koh Lanta tour that goes to the islands
4-island classicFrom US$424-Island Tour to Koh Kradan with Beach Lunch
- 4.6★ from 467 reviews
- A full day across four islands ending at Koh Kradan, lunch served on the beach
Best for: First-timers who want the archetypal 'Koh Lanta 4 islands' day
Check availability & priceThis 4-island tour ends at Koh Kradan. Confirm on the booking page whether Emerald Cave is included in the current itinerary, as operators change routes.
Frequently asked questions
On the coast of Koh Mook in Trang province, south of Koh Lanta. It is reached by boat.
Emerald Cave how to visitYes. The usual route is a swim through a dark sea tunnel, normally in a life jacket and following a guide with a torch. If you are uneasy in open water, this may not be for you.
Compare 4-island toursBoat schedules and sea conditions are less reliable from May to October. Confirm directly with your operator before booking.
Koh Lanta in the rainy seasonLast updated September 2026.
