Son Doong Cave
Hang Son Doong (Mountain River Cave) is known as the world's largest cave, and is one of the most spectacular sights in Southeast Asia. Son Doong is no day-trip destination; it's in an extremely remote area and the only way to visit is by booking a four-night/three-day expedition with around 16 porters. It costs US$3000 per person, with a maximum of 10 trekkers on each trip.
It's a cave big enough to accommodate a battleship. Sections of it are pierced by skylights that reveal formations of ethereal stalagmites that cavers have called the Cactus Garden. Some stalagmites are up to 80m high. Cavers have also discovered colossal cave pearls measuring 10cm in diameter, which have been formed by millennia of drips, fusing calcite crystals with grains of sand. Magnificent rimstone pools are present throughout the cave.
Tu Lan Cave
The Tu Lan cave trip begins with a countryside hike, then a swim (with headlamps and life jackets) through two spectacular river caves, before emerging in an idyllic valley. Then there's more hiking through dense forest to a 'beach' where rivers merge; this is an ideal campsite. There's more wonderful swimming here in vast caverns. Moderate fitness levels are necessary. Tu Lan is 65km north of Son Trach and can only be visited on a guided tour.
Hang En (En Cave)
This gigantic cave is very close to Son Doong, and both featured in a National Geographic photographic spread in 2011. Getting here involves a trek through dense jungle, valleys and the Ban Doong minority village, a very remote tribal settlement (with no electricity or roads). You stay overnight in the cave or in a minority village.
Hang Toi (Dark Cave)
Incorporating an above-water zipline, followed by a swim into the cave and then exploration of a pitch-black passageway of oozing mud, it's little wonder Hang Toi is the cave experience you've probably already heard about from other travellers. Upon exiting the cave, a leisurely kayak paddle heads to a jetty where there are more into-the-water zipline thrills to be had.
Surrounded by forested karst peaks, this remarkable cave system extends for 31km, though most people only visit the first kilometre. The scale is breathtaking, as wooden staircases descend into a cathedral-like space with colossal stalagmites and glimmering stalactites. Get here early to beat the crowds, as during peak times (early afternoon) tour guides shepherd groups using megaphones. Paradise Cave is about 14km southwest of Son Trach. Electric buggies (per person one way/return 15,000/25,000d) ferry visitors from the car park to the entrance.
Phong Nha Cave
The spectacular boat trip through Phong Nha Cave is an enjoyable, though touristy, experience beginning in Son Trach town. Boats cruise along past buffalo, limestone peaks and church steeples to the cave’s gaping mouth. The engine is then cut and the boats are negotiated silently through cavern after garishly illuminated cavern. On the return leg there's the option to climb (via 330 steps) up to the mountainside Tien Son Cave (80,000d) with the remains of 9th-century Cham altars.
The ticket office and departure jetty are in Son Trach village. Allow two hours to see Phong Nha; add an hour for Tien Son. In November and December, seasonal floods may mean Phong Nha Cave is closed. Weekends are extremely popular with Vietnamese visitors, whose presence is amplified by the spectacular echoes and unventilated cigarette smoke. Note the cave was used as a hospital and ammunition depot during the American War and was heavily bombed.
Hang Tien (Tien Cave)
The largest part of the Tu Lan cave system, this moderately challenging cave was opened to visitors in 2016. The 10- to 12-hour day adventure includes a jungle walk, and the cave is studded with verdant ferns and rimstone pools.
Hang Va (Va Cave)
Discovered in 2012, and opened to visitors in 2015, Hang Va is explored on a two-day/one-night excursion that first travels along an underground river in Hang Nuoc Nut. Tours overnight in a jungle camp at the entrance to Hang Va, where the cave's highlight is a spectacular stalagmite field partly submerged in crystalline waters. Ropes and harnesses are used extensively.