Before you enter the Emerald Cave on a Koh Lanta tour

The Emerald Cave, Tham Morakot in Thai, is the stop most people remember from a 4 Islands day out of Koh Lanta, and the one they know least about beforehand. This page covers the tide, the dark, the crowds, the park rules and fee, the closures and what to do if someone would rather stay aboard. Fees and closures were checked on 18 October 2026.

The Emerald Cave on Koh Mook at a glance

The Emerald Cave is on the west coast of Koh Mook (also spelt Koh Muk), in Kantang district, Trang province. The island is part of Hat Chao Mai National Park, a different park from Mu Ko Lanta, so the fee and the closure dates come from Hat Chao Mai.

What	What we found	How sure
Tunnel	About 80 m, dark in the middle	Secondary, consistent
Time in the water	About 10 to 15 min each way	Secondary guide
When boats can visit	Between high and very low water	Principle agreed; exact window disputed
Park fee, foreign adult	200 THB (child 100 THB)	DNP 2022 rates, secondary summary
Seasonal closure	1 to 30 September in 2026, as in 2022 and 2025	Official 2026 schedule
Suits	Calm swimmers, older children, anyone fine in the dark	Our reading of the above

On a 4 Islands tour from Koh Lanta the cave is one stop among Koh Kradan, Koh Ngai and Koh Chuak. If you are still choosing between island days, our comparison of Koh Rok, the 4 Islands and Phi Phi weighs them up.

What swimming through Tham Morakot is like

It is a slow float rather than a hard swim. The boat stops outside the cliff, you put on a life jacket and climb down into the water. Groups usually move in a line, holding a rope or staying close to a guide with a torch. The roof is low near the entrance and the middle stretch is pitch dark, then the light returns and you wade out onto coarse sand inside a ring of cliffs open to the sky.

The name comes from the green colour the water takes on when sunlight falls into the enclosure; secondary guides say it is strongest with the sun high, roughly 10:00 to 14:00. You float back out the same way. The distance is short. What unsettles people is the dark and not being able to touch the bottom.

How the Emerald Cave tide decides your time slot

The tide decides when a boat can stop, not the timetable. At high water the gap between the sea and the roof of the entrance closes, and the tunnel cannot be passed. At the lowest water the inner lagoon drains, the colour goes and the entrance can be shallow and rocky. The usable window sits between the two.

This is why sources disagree. Some say go at low tide, meaning a falling tide with headroom. Others say mid tide, meaning enough water inside for the colour. They describe the same window from different ends. Tides here come roughly twice a day and arrive about 50 minutes later each day, so the cave can be a morning stop one week and an afternoon stop the next. Around full and new moon the range is larger and the water changes faster.

Boat crews read the tide table and the swell on the day and plan the route around it. That is why the order of the islands can change. Ask us how the cave is being timed on your date rather than relying on a fixed itinerary.

Crowds and the busiest hours

Expect company. Boats come from Koh Lanta, from the Trang piers at Pak Meng and Hat Yao, and from Krabi, Phuket and Satun. Back in 2017 the park reported 3,000 to 4,000 visitors a day around the cave and nearby islands at weekends, with more than 80 tour boats working the park. We found no newer count.

Because every boat chases the same tide window, arrivals bunch together, and the middle of the day is when the colour draws the most people. Thai weekends and holidays are busier. A queue of life-jacketed groups at the entrance is normal. If a quieter visit matters to you, a private boat gives you more say over the order of the day, within what the tide allows. Our article on when a private boat trip makes sense covers the trade-offs.

Emerald Cave for non-swimmers and children

Many non-swimmers do go in, floating in a life jacket and holding the line, and some guides tow weaker swimmers along the rope. Others ask non-swimmers to stay aboard. Both are reasonable. It depends on the crew, the group size and the sea that day.

Staying on the boat is a normal choice. The cave is a short part of a long day, and the other stops can be enjoyed at your own pace. For children, think about three things: a life jacket that actually fits, an adult right beside them, and whether they stay calm in total darkness. The article on Koh Lanta with young kids covers planning days like this. Tell us ages and swimming confidence and we will check what is possible.

Park rules and the entrance fee

Hat Chao Mai National Park is in the Department of National Parks’ group 2. The rates in force from 7 June 2022 are reported as 200 THB for a foreign adult and 100 THB for a foreign child (3 to 14), and 40 THB and 20 THB for Thai visitors. We checked this on 18 October 2026 in a secondary summary of the department’s table; we could not open the department’s own page. Park staff are meant to collect the fee at the cave, so carry cash unless your tour includes it.

The rules that apply are the national ones. Under section 19 of the National Parks Act 2019, taking sand, rock, coral or other natural resources is an offence, and so is luring or harming wild animals, which covers feeding fish. Visitors must follow rangers’ instructions. A 2021 notification bans sunscreens containing oxybenzone, octinoxate, 4MBC or butylparaben in all marine national parks. Life jackets and swimming in a group are standard practice in every account we found, though we found no published park rule that sets them.

When the Emerald Cave is closed

The cave closes for part of the southwest monsoon, on dates the Department of National Parks sets each year. Its 2026 schedule closed the cave from 1 to 30 September, as park orders did in 2022 and 2025, with reopening scheduled for 1 October.

1. Jan Open
2. Feb Open
3. Mar Open
4. Apr Open
5. May Open
6. Jun Cave open
7. Jul Cave open
8. Aug Cave only
9. Sep Closed
10. Oct Open
11. Nov Open
12. Dec Open

Department of National Parks status sheet linked by TAT (data as of 7 January 2026). Koh Chuak and Koh Waen closed 1 June to 30 September, Koh Mook and Koh Kradan 1 August to 30 September, and the Emerald Cave 1 to 30 September. The 2027 dates are not yet published.

The islands around it close for longer, and some secondary guides list the cave as shut from June to September, which does not match the official dates. A past schedule does not set next season’s dates, and TAT’s notice of 15 January 2026 says closures depend on weather and park conditions. Even in an open month, boats do not run in rough seas. The 2026 schedule was signed in December 2025 and republished by TAT in January, so look for the 2027 one around then, or ask us for your date.

Your checklist before you go in

1. Before the day Tell the organiser everyone’s swimming confidence and anyone uneasy in the dark or in tight spaces.
2. Pack Water shoes, a waterproof phone pouch, cash for the park fee and a sunscreen free of the four banned ingredients.
3. Leave on the boat Valuables, jewellery, glasses you cannot lose and any camera that is not waterproof.
4. Life jacket Put it on and fasten it before you enter the water, and check children’s fit with a tug at the shoulders.
5. Listen to the briefing Note the signal to stop, the order of the line and who leads with the torch.
6. In the tunnel Keep one hand on the rope or the person ahead, kick gently and mind your head at the entrance.
7. Inside Leave the sand and shells, do not feed fish, and head back when the crew calls: the tide does not wait.

What to send us for a 4 Islands tour from Koh Lanta

We arrange the 4 Islands and other boat tours, with joined and private, longtail and speedboat options across the boat services we arrange; the format for your date is matched to the route. To get options that suit your group, message us with your preferred date and a back-up, your hotel, the number of adults and children with ages, and everyone’s swimming confidence. Say if anyone would rather stay aboard at the cave. We reply with what runs on your date, how the stops fit the tide, the price and which park fees are included.