Ang Thong National Marine Park is an archipelago of 42 jungle-covered limestone islands in the Gulf of Thailand, about 30 km west of Samui. There's an emerald saltwater lake hidden inside Ko Mae Ko, a viewpoint that takes in the whole island chain, kayaking and snorkelling — all doable as a day tour from Samui or Koh Phangan. We'll be straight about everything, including the months the park closes for the monsoon.
If we could pick only one day trip from Samui, this would be it every time. Ang Thong National Marine Park (Mu Ko Ang Thong) is a cluster of 42 limestone islands in the Gulf of Thailand, part of Surat Thani province, about 30 km west of Samui. The view of green karst islands strung across the sea from the park's viewpoint — the photo at the top of this page — is the defining image of the Gulf, and the islands here are often said to have inspired Alex Garland's novel The Beach.
The first thing to know: there is no public ferry to the park. Everyone visits on a day tour (hotel pick-up around 7.00–8.00 am, back around 4.00–5.00 pm) or by private charter. A standard tour day covers the Emerald Lake, the viewpoint, kayaking, snorkelling and lunch. The real decision is big boat or speedboat — we compare them honestly in card 5 below. Still weighing whether Ang Thong deserves a day of your trip? Skim our list of things to do on Koh Samui first — though we'll spoil it: this is at the top.
In the order most tours visit them, with an honest note on what's genuinely special, what's hard work, and what costs extra.
The park's most famous sight. Thale Nai, the "inner sea," is an emerald saltwater lagoon hidden in the middle of Ko Mae Ko, ringed on every side by sheer limestone walls — as if nature had scooped a basin out of the island. The lake connects to the open sea through underwater passages in the rock, so its level rises and falls with the tide even though you can't see any channel at all.
The way up is a steep staircase of about 10–15 minutes with handrails the whole way, and the moment you reach the platform you understand the fuss. To be clear up front: swimming is prohibited — it's a conservation zone, viewed from above only. Mid-morning, passengers from several boats arrive at once; if your tour lands early, head straight up.
Ko Wua Talap is the park's main island (the headquarters is here) and home to the viewpoint over the whole archipelago — the postcard of Ang Thong everyone comes for. The trail is about 500 metres, which sounds short, but it is genuinely steep, with sections of bare rock where you haul yourself up on ropes. Allow about 30–45 minutes to the top, roughly 350 metres above the sea.
Honestly: it's sweaty and hot. Wear real shoes, carry water, and don't force it — the white-sand beach at the bottom is lovely enough to wait on while your group climbs. If you do make it up, the hero photo on this page is our guarantee that it pays off.
Many of Ang Thong's best angles only exist at water level — paddling under limestone overhangs, through rock arches and into small coves the big boats can't reach. If you can, pick a tour that includes kayaking. You paddle as a guided group, no experience needed, two to a kayak.
Check carefully when you book: some tours include kayaking in the price, others charge about ฿300–500 extra, and a few kayak-focused tours give you much longer on the water. Life jackets stay on throughout. Long sleeves and a hat will save you from the sun, and your phone belongs in a waterproof pouch before it comes anywhere near the kayak.
Most tours include a snorkel stop, usually around Ko Wao at the northern end of the park — shallow coral and plenty of fish, with masks and snorkels lent out on board.
We'll say this plainly so nobody is disappointed: the Gulf water here is not as clear as the Andaman or Koh Tao, and visibility depends on the season and recent rain. If snorkelling or diving is the main point of your trip, make a Koh Tao–Koh Nang Yuan trip your headline day and treat the Ang Thong snorkel stop as a bonus. As part of a general day out, though, it's good fun — especially with kids.
Speedboat — fast (~45 min–1 hr each way), more time in the park, smaller groups, higher price at about ฿1,900–2,900. The trade-off: it slams over the waves, and on a choppy day that gets tiring fast. If you're prone to seasickness, think hard.
Big boat / double-decker — slower (~1.5–2 hr) but far steadier, with room to walk around, toilets and shade. Best for families, older travellers and anyone with a delicate stomach, at a gentler ฿1,400–2,000. Both usually include lunch, fruit, water and snorkel gear, and usually exclude the national park fee (foreign adults ~฿300, children ~฿150 — cash on arrival). Always read the inclusions when you book.
Based on Koh Phangan? No need to relocate to Samui first — many Ang Thong tours also depart from Thong Sala pier, the distance is similar, and the programmes and prices are much the same.
And if you'd rather not share the park with the tour boats at all, there's an option most visitors never hear about: Ko Wua Talap has national-park bungalows and a campsite near the headquarters, booked in advance through the Thai national parks system. In the early morning and late afternoon, after the boats leave, the island is yours. We'll be honest — facilities are very basic (generator power at set hours, food from the park canteen) — but a sunset on an empty beach is a fair trade.
Book the right tour — always read the inclusions before paying: is the park fee included (usually not)? Is kayaking included? Does pick-up cover your hotel zone (Chaweng, Lamai, Bophut and Maenam are usually free; outlying areas may cost extra)? Outside high season, booking 1–2 days ahead is fine; in January–April give it 2–3 days. And if the wind picks up, tours cancel and refund or rebook you — annoying, but better than forcing a rough crossing. Build a spare day into your plan (our 3-day Samui itinerary slots Ang Thong early in the trip for exactly this reason).
What to bring: seasickness tablets (take them ~30 minutes before boarding — Gulf chop on a windy day is no joke, especially on a speedboat), proper shoes or strapped sandals for the viewpoint, swimwear worn from the hotel, a towel, sunscreen, a hat, sunglasses, a waterproof phone pouch, and cash for the park fee and drinks on the island. Leave anything precious at the hotel.
The season matters more than anything on this trip: Samui is on the Gulf coast, so its rainy season is the reverse of Phuket and Krabi. The sea is at its best January–April, with a second good window June–August; the heaviest rain falls October–December (November worst of all), and the park closes for the monsoon roughly November–December every year — dates vary and are announced by the national park authority, so check before you even book flights for a year-end trip. For the month-by-month picture, read our guide to the best time to visit Thailand.