🔄 Updated 21 Jun 2026
The Emerald Cave is on the west side of Koh Mook in the Trang sea — a limestone cave whose mouth opens onto the water, but the entrance hides beneath a cliff. From the boat it looks like nothing more than a small gap. Once the boat pulls up out front, everyone gets in the water, puts on a life jacket, and swims through a dark tunnel roughly 80 metres long. The middle of the tunnel is pitch black, so you rely on the guide's torch to lead the way. Come out the far end and you reach a small white-sand beach hidden in the centre of the island, walled in by tall rock and green trees — a tucked-away spot you can't see at all from outside.
What Is the Emerald Cave, and Why Do People Want to Go?
What sets the Emerald Cave apart from a typical sea destination is the way you get in, not just the view at the end. Swimming through the cave in total darkness alongside dozens of other people, with only a rope and the guide's torch to follow, is the most thrilling stretch of the trip. As the light at the end of the tunnel starts to creep in, the water slowly turns emerald green from sunlight refracting through the sea, then opens out to a hidden beach so quiet and pretty that a lot of people say it's worth the effort.
- Tunnel about 80 metres long — pitch black in the middle, so you swim behind the guide and follow the rope
- Hidden beach in the island's heart — white sand walled in by tall cliffs, invisible from outside the island
- Emerald-green water — created by sunlight refracting through the water in the cave, clearest from mid-morning to noon
- Open only at low to mid tide — at full high tide the tunnel gets too low to get through
Can You Go If You Can't Swim?
Yes. Everyone wears a life jacket anyway, and the local guides lead you through in a group with a rope to hold onto, so non-swimmers can float along holding the rope. But if you're afraid of tight or very dark spaces, weigh it up first — the middle of the tunnel is pitch black and there are a lot of people in it.
Want more out of Trang? Book tours & activities
Booking online ahead on Klook or GetYourGuide is usually cheaper than the gate and skips the queue. Pick only the experiences you actually want — prices and availability are shown live on each site.
How to Get to Koh Mook and the Emerald Cave
The Emerald Cave is on Koh Mook, and there are two main piers to leave from the mainland: Pak Meng Pier (Sikao district) and Kuan Tung Ku Pier (Kantang district). It's about 40 kilometres from Trang Airport to Pak Meng Pier, an easy drive or car rental. Most people don't take a boat to the cave on their own — they buy a day-trip tour that bundles the Emerald Cave with other islands in a single run.
- Join-in group day trip — the most popular option, leaving from Pak Meng, combining the Emerald Cave, Koh Kradan, and Koh Chuek in one day
- Passenger boat to stay on Koh Mook — board at Kuan Tung Ku Pier, about 30 minutes, good if you want to stay overnight on the island
- Private longtail boat charter — flexible on timing, you pick which islands to stop at, good for small groups
- Rent a car from Trang town — drive to the pier yourself and join a tour there, cheaper than a transfer if there are a few of you
Rough Tour Prices
Prices depend on the type of trip and the season. The figures below are rough estimates from local operators — check again with whoever you book through, since they shift with the time of year and the number of people.
Join-in 4-island tour (Emerald Cave–Koh Kradan–Koh Chuek–Koh Waen)
The option most people pick. It leaves Pak Meng Pier in the morning, stops at the Emerald Cave so you can swim through to the hidden beach, then carries on to snorkelling at Koh Chuek and Koh Waen before lunch and swimming at Koh Kradan, getting back to the mainland in the afternoon. The price covers the boat, snorkelling gear, life jacket, and lunch.
Private longtail boat charter (Emerald Cave + Koh Kradan)
You charter the whole boat and choose your own stops and timing — good for a small group or family that doesn't want to go with a big crowd. Priced per boat by the number of people, and it includes drinking water, snorkelling gear, and life jackets.
Large double-deck boat tour (busier join-in group)
A big tour boat that's comfortable to sit on, good for anyone who wants a steadier ride that doesn't rock much. The route is similar to a standard join-in trip, with the Emerald Cave as the highlight, and the price is close to a longtail join-in.
Koh Mook overnight package, 3 days 2 nights
For people who want to make the most of the Trang sea. It bundles a stay on Koh Mook, an Emerald Cave tour, and trips to outer islands like Koh Rok, with boat transfers and several meals. Worth it if you've come a long way and want a longer trip.
Book Ahead or Sort It Out on the Day?
Over long-weekend high season, tours fill up fast, so book at least 1–2 days ahead — especially if you want a morning run that enters the cave as the tide is dropping. On quiet weekdays off-peak you can walk up and book at Pak Meng Pier on the day, but be ready for the chance you won't get the slot you wanted.
Timing and the Season You Can Go
Timing matters a lot with the Emerald Cave, because you can only get in at low to mid tide. At full high tide the tunnel gets too low to swim through, and tours adjust their departure to each day's tide chart. As for the emerald-green colour inside, it's clearest when the sun is shining onto the beach — roughly mid-morning to noon.
- Open season: roughly November to April, when the sea is calm and boats run every day — the best window
- Closed season: roughly May to October, the Andaman monsoon, when the sea is rough and the Emerald Cave is usually off-limits for safety
- Cave entry time: depends on that day's tide chart — tours schedule runs to match the low-to-mid tide window
- Emerald water at its clearest: roughly 10:00–14:00, when the sun reaches the beach inside the cave
Avoid the Crowded Slots
The Emerald Cave is narrow and gets crowded easily. Mid-morning, several tour boats often arrive at once, so you end up queuing to swim through and the beach inside gets packed. If you charter your own boat or take a tour that leaves a bit earlier, you've got a better shot at reaching the cave while it's still quiet and getting nicer photos of the hidden beach.
What to Prepare and Pack
Waterproof your valuables
Phone, camera, and wallet need to go in a dry bag — you're swimming through the cave, so they'll get wet for sure.
Heel-strap water shoes
The beach floor inside the cave and some of the rocks are slippery — water shoes make walking easier and help avoid cuts.
Waterproof camera / GoPro
The angles in the tunnel and at the hidden beach photograph well, but it's dark inside, so use a camera that handles low light.
Reef-friendly sunscreen
It helps protect the corals of the Trang sea — a formula that doesn't harm the reef is better for the water.
Pair the Trip with Nearby Islands
The Emerald Cave usually isn't a stop on its own — it sits on a Trang island route that pairs up nicely, so you can see several spots in a single day.
- Koh Kradan — white sand and clear water with good snorkelling, the lunch and swim stop on most tours
- Koh Chuek — a snorkelling spot for colourful soft corals, plenty of fish, and clear water, close to the Emerald Cave
- Koh Mook (village-side beach) — if you stay on the island, there's a quiet beach, local restaurants, and sea-gypsy life
- Koh Libong — Trang's largest island, with dugongs and seagrass, good for a separate day trip
Plan a full Trang islands trip covering the Emerald Cave and the islands around it
See the Trang travel guide →