Discover the magnificent caves in Vietnam.

Quang Binh province in central Vietnam is particularly famous for Phong Nha-Ke Bang National Park, also known as the "Kingdom of Caves". Last year alone, the area welcomed 3.9 million tourists, an increase of 18.2% compared to the previous year.

"Vietnam possesses some of the most spectacular caves in the world. The average annual temperature is stable, the forest landscapes are incredibly beautiful, and the structure is absolutely stunning. Importantly, they are incredibly pristine and intact, with nothing having been destroyed," Howard Limbert, a technical consultant at Oxalis, a tourism company based in Quang Binh, told CNN.

"My team (the British Cave Exploration Association) has explored over 500 caves in Vietnam. But we've only explored about 30% of the area. There are many, many more caves waiting to be discovered."

For those fascinated by Vietnam's underground world, here is a list of worthwhile destinations to consider:

Son Doong Cave and En Cave

Considered the largest cave in the world, Son Doong Cave currently measures 38.5 million cubic meters. This enormous cave system even contains an entire primeval forest inside.

Following the trail of Son Doong Cave, explorers continued to discover that it is connected to another cave called Thung Cave via an underground river, potentially increasing the cave's size by an additional 1.6 million cubic meters.

Oxalis Travel, in partnership with the Royal British Cave Exploration Association, has been licensed to organize tours into this cave, with an average group size of 6 to 10 people for a 4-day trip. Tours are typically held during the dry season, from January to August each year.

On the first day of the tour, visitors will trek through the primeval forest inside the cave for an hour before stopping for lunch at Ban Doong village.

After a few hours of hiking, the group will set up tents inside En Cave (the third largest cave in Vietnam), where visitors can swim in the rivers flowing through the cave and enjoy traditional Vietnamese dishes.

The following day, the explorers will continue their journey to reach the 80-meter-high rock ledge inside the cave, which can only be climbed using ropes.

Once inside the cave, visitors will immediately be able to explore the rich system of stalactites and underground river systems throughout the two-day tour.

Va Cave and Nuoc Nut Cave

Besides the Son Doong tour, Oxalis also offers tourists a 2-in-1 tour package that visits both Va Cave and Nuoc Nut Cave.

On the first day, you will hike 2km to Nuoc Nut Cave, which contains a unique underground river system. Swim 100m across the river to reach Va Cave and camp there overnight.

Although more accessible and easier to conquer than Son Doong Cave, exploring these caves still offers many exciting adventures as you trek through forests, climb over rocky outcrops, and swim through treacherous underground rivers. Va Cave, in particular, is famous for its rugged stalactite formations.

Tu Lan Cave System

Comprising more than 10 large and small caves in Quang Binh province, the Tu Lan cave system quickly gained fame since 2017 after the blockbuster "Kong: Skull Island" was released and created a sensation among fans worldwide.

"Many people came here because of the movie, but in the end they discovered that the scenery here is even more beautiful than they imagined," Limbert told CNN.

"All tours camp near a lake or waterfall, so it's great for visitors to swim in the cool weather. On the Tu Lan tour, you'll enter through this cave entrance and exit from the forest side of another cave."

Oxalis currently offers tours ranging from 1 to 4 days, depending on the area and the flexibility of the visitor's schedule.

"In this area, we need to maintain tight control, so you'll see very few people. But this also means the whole cave seems to belong to you alone," Limbert continued.

Within the Tú Làn cave system, one of the most famous attractions is the Fairy Cave, named after its shape, which resembles vast rice paddies with towering rock formations.

Crossing through two caves, including Tien Cave 1 and Tien Cave 2, your guide will lead you through a vast forest, a dry cave stretching 5.5km and reaching a height of 100m at its peak.

"These caves are drier than others in the same area, so they're popular with tourists who don't want to swim during the tour," Limbert shared.

Paradise Cave

Another stunning cave located within the Phong Nha - Ke Bang National Park system is Paradise Cave.

A local man discovered the cave's entrance in 2005, which was initially just a small hole in a rock slab. Soon after, the British Cave Exploration Society explored the inside of the cave and was amazed by its stunning beauty.

Currently, Thien Duong Cave is one of the most popular tourist attractions in Vietnam. It is considered the longest dry cave in Asia, with a total length of 31km, and moreover, it is a very spacious cave, large enough to fit an entire jet plane.

Visitors can explore this cave complex in two ways: by walking 1km up the wooden steps or by staying overnight and undertaking a 7km trekking trip.

"I always encourage and recommend people join the 7km trekking tour because it gives them plenty of time to experience and spend at least 6 hours in the cave exploring to their heart's content. It's truly an unforgettable experience."

Tam Coc Cave

Besides Quang Binh province, the UNESCO-recognized Trang An cultural complex is also very famous with tourists from near and far. Located in Ninh Binh province in northern Vietnam, it is another prominent destination where tourists can explore fascinating caves.

"What I like most about the caves in Vietnam is that each one has its own unique characteristics," Nguyen told CNN.

"The journey is part of the experience. Therefore, the way you get to the cave system here makes the experience even more special. You can hike, climb, swim, or take a boat. Each option offers a completely different experience."

This is especially true when you explore the Tam Coc cave complex (meaning "three caves") in Trang An. Tam Coc comprises three caves: Hang Ca, Hang Hai, and Hang Ba, all accessible by boat departing from Van Lam village.

A gentle, 3km boat ride will take you smoothly along the Ngo Dong River, past rice fields and limestone formations, before reaching the cave system.

Hang Ca is the largest of them, measuring 120m in length, while Hang Ba is the smallest, with a total length of 45m.

"Because you can only get through the cave by boat, this trip will be very relaxing and accessible to all tourists," Nguyen added.

"The ideal time to visit Tam Coc is from March to May, when farmers begin planting rice in the fields. It's a magical sight of a sea of ​​green and golden rice paddies."

Surprise Cave

Ha Long Bay may be most famous for its system of towering limestone mountains rising above the bay, but it also boasts countless caves that you simply can't miss. The list of caves here has been updated to 59.

Among them, Sung Sot Cave is the most famous. Located on Bo Hon Island in Ha Long Bay, this cave was first discovered by a French explorer in 1901.

Spanning an area of ​​up to 10,000 square meters, this cave is incredibly large, boasting a magnificent system of stalactites and stalagmites in many unique shapes, such as funnel-shaped and flower-like.

There are many stories and folklore surrounding the shape of the stalactites, and it would take an hour or two to explore them all.

Luon Cave

Although smaller than Sung Sot Cave, Luon Cave gives you the feeling of a secret gateway leading you to the wondrous world of Ha Long Bay.

The cave is 60 meters long and 4 meters high, and can only be reached by kayak or small boat. When the water level rises, the cave entrance becomes very small and even more difficult to enter.

Inside, this cave offers a cool, refreshing atmosphere, with crystal-clear blue water and narrow passages that create a sense of mystery.

On the other side of the cave is a lake surrounded by limestone formations, home to a population of wild monkeys, creating a truly spectacular panoramic view.

Nga Nguyen