Dark Cave (Hang Toi) sits on the Chay River inside Phong Nha-Ke Bang National Park, and the park's tourism center runs it as an activity site rather than a sightseeing cave. The management board says the cave was found in 1990 and is not known for grand stalactites. People come for what you do there: a zipline across the river to the cave mouth and a natural mud pool deep inside, which the board calls the only cave mud bath in Vietnam.
On the explore package you are fitted with a harness, life jacket and caving gear, then ride the twin zipline about 400 m across the Chay River, landing near the cave mouth. Inside you explore the cave on to the mud pool, formed from fine mineral mud that builds up in the rainy season. Afterwards you come back to the river for kayaking, a shorter zipline that drops you into the water, a jump bridge, a water slide and other games. The board says to allow about four hours, depending on the package.
No freely licensed photos of Dark Cave or the Chay River site are on Wikimedia Commons, so the pictures on this page show the park and the Son River around Phong Nha, not the cave itself.
Getting there
Dark Cave is about 7 km in a straight line from Phong Nha town and about 3 km from Phong Nha Cave, upstream on the Chay River. It is about 38 km in a straight line from Dong Hoi railway station. You buy your ticket at the site, where staff explain the packages before you pay and hand out the safety gear for yours.
Hours and fees
The site opens every day, from 07:45 to 16:30 in summer and from 08:00 to 15:30 in winter. The board does not say which months count as summer and winter.
| Package | Adult | Child 1.1 m to 1.3 m |
|---|---|---|
| Explore: 400 m and short zipline, Dark Cave, mud bath, kayak, river games | VND 450,000 | VND 150,000 |
| Standard: 400 m and short zipline, kayak, river games, no cave | VND 220,000 | VND 110,000 |
| River play: short zipline, kayak, river games, no cave, no 400 m zipline | VND 150,000 | VND 110,000 |
We read these prices on the board's page on 18 October 2026. The adult prices and the explore child price match what the page showed on 14 October.
Rules worth knowing before you go:
- The mud bath needs a height of 1.1 m or more, and the 400 m zipline a weight over 40 kg. Children under 1.3 m or 40 kg get a separate swimming and play area.
- The board advises against it for people with heart problems, high blood pressure or weak joints, for pregnant women and for anyone afraid of heights.
- For the mud bath the board asks women to wear a two-piece swimsuit and men swim shorts. Bring a towel and a change of clothes; waterproof phone pouches are sold at the site.
- The site can close in heavy rain, floods or storms. On 30 October 2025 the park's tourism center stopped taking visitors at Dark Cave and its other river sites until further notice after long heavy rain, so check its Facebook page in the wet months. Our Phong Nha weather in the wet season guide covers when that happens.
The site's hotlines are 0918 841 455 and 0868 815 678. Our Phong Nha Cave ticket price article compares the cave tickets in the park.
Our take
Come here for an active half day, not for cave scenery. The explore package is the one to buy: the standard ticket saves VND 230,000 but leaves out the cave and the mud bath, which are the reason the place is famous. Wear a swimsuit under your clothes, leave valuables behind, and if you are under 40 kg or not keen on heights, the river play package keeps the kayaks and the water slide without the long zipline.
Nearby
- Phong Nha Cave: about 3 km in a straight line, the boat cave near town.
- Paradise Cave: about 7 km in a straight line, a dry cave on a long boardwalk.
- Son Doong: about 13 km in a straight line, reached only on a multi-day expedition.
