• Duration: Four days
• Distance: 25km (8km caving)
• Difficulty: Moderate
• Accommodation: Camping
• Start/end point: Phong Nha Village

The British Cave Research Association helped launch this tour with Oxalis Adventure, a local company, with limited numbers and a strict route to protect the integrity of the cave. This includes guides, porters, a cave expert and food, and it remains the only way to explore Son Doong Cave.

Son Doong is a unique trekking experience, with underground jungles, giant ceiling collapses, ethereal campsites and stalagmites the size of multi-storey buildings. If you think caving is crawling around in narrow spaces, think again – some of these chambers can fit aeroplanes with room to spare.

Whenever I mention the Son Doong Expedition, people usually question the expense of the all-inclusive tour – USD $3,000 – and I always say the same thing. Yes, it’s expensive, especially for Vietnam. But this cave is one of the world’s great wonders. Many people are happy to pay that much to go skiing in the Alps for a week – and the Son Doong Cave Expedition surely beats that.

If the Son Doong Expedition is over budget, consider one of more than a dozen other caving experiences in Phong Nha-Ke Bang National Park, including the hike to En Cave, Pygmy Cave or the Tu Lan cave system.