Son Doong Cave

Son Doong is the largest cave on earth by volume, and the first thing to settle is whether you can actually go. Entry is only possible on a multi-day expedition with Oxalis Adventure, the sole licensed operator, at roughly 79,500,000 VND per person. About a thousand permits are issued a year, the season runs January to August, and departures have been selling out years in advance. If you are planning a trip for this season or next, the honest answer for most people is no, and the later part of this page covers what to book instead. If you are willing to plan years ahead and pay for one of the great expeditions in world travel, read on.

The scale is the point, and the numbers only begin to mean something when you try to picture them. Passages run up to about 200 metres tall and 150 metres wide, room enough for a skyscraper lying on its side with air to spare above it. Where sections of the ceiling collapsed long ago, the dolines left behind let in enough light for jungle to grow on the cave floor, full trees rooted far underground with birds moving between them. The cave is large enough to make its own weather: clouds form inside the biggest passages, and expedition photographs regularly show mist drifting beneath a stone roof. That detail sounds like marketing copy and is simply documented fact, which is Son Doong in general: the claims that read like exaggeration are the surveyed ones.

What the money buys is a genuine expedition rather than a hard hike. The fee covers the permit, guides, safety staff, porters, food and camping, with nights spent inside the cave itself. Reaching the entrance means trekking through the jungle of Phong Nha-Ke Bang National Park with river crossings along the way, and nothing inside is built for visitors: no boardwalk, no lighting, no handrails, just wet rock, sand and the route your guides set. It is demanding rather than technical, and fit regular walkers complete it, but it deserves honest preparation.

The access rules are absolute. One operator holds the licence, and any other company offering Son Doong is reselling or misleading you. The season is January to August only, because the river inside rises in the flood months and the cave closes. There is no day trip, no shortened version and no viewpoint from which you can see anything at all: it is the full expedition or nothing.

Which brings most readers to the real decision: what to book instead this season. Hang En is the closest sibling, the third-largest cave on earth, on the same river system and run by the same operator, with a night camped on a sand beach inside it for about 8,800,000 VND over two days, and it can usually be booked for the season you are actually travelling in. Hang Pygmy is the fourth-largest cave in the world by volume, and sleeping inside its chamber costs 7,900,000 VND on a two-day trip for anyone 15 or over. Kong Collapse is the hardest trip in the park, five days ending in a 100 metre rope descent into Vietnam's deepest sinkhole, at 35,000,000 VND. None of them is Son Doong, but each delivers a large share of what people actually want from it, in the year they want it, and none carries a waiting list measured in years.

Getting to the region is the same for every cave here. Dong Hoi is the gateway, with an airport and a mainline station about 45 km from Phong Nha town: 45 to 90 minutes by taxi, or around 90 minutes on the local bus for about 35,000 VND. Trains reach Dong Hoi in about 3 hours from Hue, 4 to 5 from Da Nang and about 10 from Hanoi, where the overnight sleeper is the comfortable option. The regional dry season runs February to August with March and April the sweet spot, floods from September to November close the expedition caves, and cave interiors hold around 23C all year, so conditions underground are kinder than the jungle outside.

Don't miss

• Largest cave on earth by volume, with passages up to about 200 metres tall and 150 metres wide
• Jungle growing on the cave floor beneath collapsed sections of ceiling
• Large enough to generate its own weather, with clouds forming inside the biggest passages
• Found in 1990, lost for years, refound in 2008 and surveyed in 2009
• Roughly 1,000 expedition permits a year, run solely by Oxalis Adventure
• Season January to August, about 79,500,000 VND per person, booked years ahead

Good for

Getting there

Know before you go

• One operator only, Oxalis Adventure. Any other company offering Son Doong is reselling or misleading you.
• The season is January to August. The cave closes when the river inside rises.
• Roughly 1,000 permits a year, and departures have been selling out years in advance, so this is a trip you plan years out, not months.
• You cannot see Son Doong on a day trip or from a viewpoint. It is the full expedition or nothing.
• The fee of about 79,500,000 VND covers permit, guides, safety staff, porters, food and camping, so there is little extra to budget beyond reaching Phong Nha.
• Train for it. The route is demanding rather than technical, but you will be trekking jungle and crossing rivers for days.
• The interior holds around 23C year round, so pack for cool nights at camp as well as jungle heat outside.

A bit of history

Ho Khanh, a local man, found the entrance in 1990 while sheltering from a storm, and then could not relocate it afterwards: the doorway to the largest cave on earth was simply lost in the jungle. He found it again in 2008, and in 2009 a British Cave Research Association team surveyed the cave and confirmed it as the largest in the world by volume. The gap between those dates is the detail worth sitting with. The record holder went missing for eighteen years because one man could not retrace a walk through dense forest. Tourism arrived later under a strict permit system of roughly a thousand places a year, which is why the discovery story is now inseparable from the booking story: the world learned about Son Doong far faster than the queue to enter it can ever move.