Enchanting underworld: The Tu Lan Jungle and Cave Exploration Tour allows travellers to climb and swim through massive underground caves. — Photos Ryan Debood

by David Mann

It's unfortunate to admit, but travelling through Viet Nam can sometimes be hit and miss. As a fairly seasoned explorer, I've had my fair share of blips on the itinerary, like Hai Phong or "grim Vinh", which warrant at most no more than a few hours.

On the flip side, however, are truly remarkable places like the Tu Lan Cave system in Quang Binh Province. If you are looking to get the heart rate pumping and the adrenalin flowing, then this province is surely for you.

Quang Binh is home to the world's largest cave, Son Doong, which was included on the New York Times' list of 52 Places to Go in 2014. This international fame means that the region is now on the bucket list for many adventure tourists - good news for travel company Oxalis, which hosts regular tours to the Phong Nha-Ke Bang National Park.

But with places in high-demand, and going at US$3,000 a pop, I decided to use some of my hard-earned freelance journalist income on the much cheaper option of a two-night, three-day tour through Tu Lan.

Great outdoors: The tour includes a total trek of 18km across steep limestone mountains and through some of the biggest caves in Phong Nha-Ke Bang National Park.

The Tu Lan Jungle and Cave Exploration Tour takes tourists through the same UNESCO World Heritage listed national park, home to 300 caves and one of world's largest limestone karst regions. It offers the same thrills as the Son Doong tour, it's just that the caves could house one football stadium rather than two.

The caves are nestled near the Laos border, around 70km north-west of Phong Nha, and are reachable by a one-hour transfer provided by Oxalis. After a safety briefing and double bagging that should ensure your belongings are water-proofed, the adventure begins.

The tour starts at Tan Hoa village with a 2km trek across the peanut fields to the Rao Nan River. After crossing the river, the climbing begins as you scale the rocky hillside to Sinh Ton valley, following the trail and mountain ridge up to Mango Mountain.

Jungle fever: The tour gives you plenty of time to soak in the jungle atmosphere.

From here, we had a spectacular view of the surrounding landscape: lush, tropical rainforest and the Rao Nan River snaking its way through rolling valleys. A distinctive high watermark can be seen on all the mountains in the area, a recurring legacy of the annual floods. During the monsoon season, the entire valley acts as a bowl and the caves are the only source of drainage to ease the flooding.

After less than an hour, all traces of civilisation had vanished and we were deep in the jungle, surrounded by thick ground cover and massive limestone formations. We travel back in time as our English-speaking guide explains that many locals have lost their limbs stepping on unexploded bombs left behind from the war.

The tour continues traversing across steep limestone mountains to reach five major caves in the area, including Tu Lan, Kim and Ken, which snagged National Geographic's Photograph of the Year in 2011. It should be said that the climbing isn't for the faint-hearted.

However, the real highlight is the swimming. Donning head torches, our waterproof bags and our trekking boots, we began the first swim through Tu Lan cave.

Few words can describe what it's like to float through a massive underground cave that is millions of years old. A soft current pushes you through the caves as you take in another world of epic formations and swim through the underground rivers. Occasionally, your feet touch the bottom, but for the most part, you are floating and swimming your way through the mountain. Superb!

For a moment, we turn off our torches to embrace complete darkness and an eerie silence. Our guide jokes about underwater monsters, prompting some nervous laughs and the torches to flick back on.

After a day trekking and climbing, we arrive at our riverside camp absolutely exhausted. I was so tired that I could have fallen asleep on a jagged rock, but thankfully the porters had already set-up our hammocks for the night.

Our entire next day of ‘caving' was spent climbing, diving and crawling through some of the world's most exquisite and remote caves. Everything is so well-preserved that you can imagine exactly how it would have looked thousands of years ago.

On the second night we camped by Hung Ton waterfall in the To Mo Valley, allowing us to spend the afternoon basking in the clean jungle air and the pristine streams running by the campsite – and it's not often that I'm comfortable swimming in Vietnamese rivers.

Viet Nam's famed cuisine extended to our delicious evening barbeques, which our friendly jungle porters from the local minority village cooked up while passionately belting out entertaining folk songs. Definitely a highlight.

With two nights camping in the great outdoors you will have plenty of time to soak in the jungle atmosphere and learn more about the local people of the area. This is not a walk in the park and it is setup as a real jungle adventure. You will swim through caves, traverse wide rivers, and negotiate rocky trails, but it will no doubt be a highlight of your travels in Viet Nam. — VNS