Son Doong is the largest known cave passage in the world by volume. Its main passage is more than 5 km long, 200 m high and 150 m wide, and a British Cave Research Association survey in April 2009 put its volume at 38,500,000 cubic metres. Some stalagmites inside are up to 80 m tall. In two places the ceiling has collapsed into giant dolines, and sunlight falling through them has grown a forest inside the cave.
A local man, Ho Khanh, found the entrance on 10 December 1990 while looking for agarwood, lost it, and found it again in 2008. In 2009 he led the British cavers to it. Their survey stopped at a flowstone wall about 60 m high that they named the Great Wall of Vietnam, and they crossed it in 2010 to reach the end of the passage. The first paying visitors went in during August 2013.
You cannot visit on your own. Permits are limited and issued from January to August, and since 2017 only Oxalis Adventure has permission to take tourists into the cave. The park management board lists Oxalis as the company running the Son Doong expedition with it.
The expedition
Oxalis sells the trip as six days and five nights: a hotel night in Phong Nha before and after, and three nights camping in between, one in the forest near the entrance and two inside the cave, at the first and second dolines. On the first trekking day you leave Phong Nha at 08:00 for the trailhead on the western branch of the Ho Chi Minh Highway, walk 14 km with about 30 knee-deep river crossings, pass Ban Doong village and go through Hang En on the way to camp.
Over the whole trip Oxalis counts 28 km of jungle trekking with height changes up to 800 m, 9 km inside the cave, an 80 m roped descent from the entrance to the cave floor, and a 90 m climb out over the Great Wall: an 18 m ladder, then 72 m of rock on a 45 degree slope, with ropes and safety staff. Each group of 10 guests goes with a cave expert, a guide, six safety assistants, two cooks and 18 porters. Porters carry up to 7 kg of your gear to camp; you carry a daypack.
Getting there
Son Doong is about 17 km in a straight line from Phong Nha town and about 33 km from Dong Hoi railway station. You cannot get there independently: Oxalis picks guests up in Dong Hoi, about 45 km from Phong Nha by its count, and drives the group to the trailhead on the first trekking morning.
Hours and fees
| Son Doong expedition (Oxalis) | Details |
|---|---|
| Price per person | VND 80,000,000 (US$3,000) |
| Included in the price | VAT, the US$600 entrance and environment fee, the US$20 park management fee, guides, porters, meals, two hotel nights, three camping nights, basic travel insurance |
| Season | January to the end of August only |
| Length | 6 days, 5 nights |
| Cancellation | At least 90 days before departure, with a VND 7,000,000 fee per person |
We read these on Oxalis's page on 18 October 2026. The same page says the 2027 and 2028 departures are fully booked, and in another paragraph that 2028 still has limited places, so expect to book two years or more ahead and ask Oxalis which dates are open. Wikipedia notes the cave is closed to tourism from September to December, when heavy rain raises the underground river.
Oxalis rates the trip as its most challenging. To be accepted you must have done at least one overnight trek with camping in the last 12 months, with days of 8 km or more over rough rocky ground and 1,000 m of climbing, and be able to climb five flights of stairs without stopping or run 5 km on the flat in under 45 minutes. It says the trip may not suit people with heart conditions, blood pressure above 140/80, diabetes or joint and bone problems, and it can cancel a booking without refund if the health details you give turn out to be false.
Hang En, the easier option
Hang En is the cave you walk through on the way to Son Doong, about 3 km in a straight line from its entrance. Oxalis calls it the third-largest cave in the world, 1.6 km long, with a campsite about 700 m inside under a ceiling up to 140 m high. It sells a separate trek there, two days and one night with a night camping on the sand inside the cave, and the park board lists Oxalis for the Hang En route too.
| Hang En trek (Oxalis) | Details |
|---|---|
| Price per person | VND 9,500,000 (about US$358), for departures from 15 November 2026 |
| Season | December to mid-September |
| Length | 2 days, 1 night |
| Distance | 25 km of trekking, 3 km of caving, a 450 m climb out at the end |
| Group size | Up to 16 guests |
| Cancellation | Full refund up to 7 days before departure |
Oxalis rates it moderate: within the last 12 months you need one overnight trek, or one or two day hikes of 6 km or more on steep jungle ground with 500 m of climbing, and the same stairs or 5 km run test as for Son Doong.
Our take
If you have the money, the fitness and the patience to book years ahead, Son Doong is unlike any other trip in Vietnam, and the price covers a team of about 30 people for each group. Train for it: the river crossings on day one and the climb up the Great Wall on the last day are where people struggle. For most visitors Hang En is the realistic choice. It is the same valley, the same first-day walk past Ban Doong and a night camped inside a giant cave, at about an eighth of the price and with dates you can still get.
Nearby
- Paradise Cave: about 10 km in a straight line, a dry cave anyone can walk on a boardwalk.
- Phong Nha Cave: about 14 km in a straight line, the boat cave near town.
- Dark Cave: about 13 km in a straight line, zipline and mud bath on the Chay River.
