Located in the heart of the Phong Nha-Ke Bang World Natural Heritage, Quang Binh, the Hung Thoong cave system includes many caves such as: Tron cave, Hung cave, mountain lake, Thung cave and Ac Mong sinkhole.

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The Nightmare Sinkhole is located in the Hung Thoong cave system. Photo: Jungle Boss

To date, only a handful of explorers have set foot at the bottom of the Nightmare Sinkhole, so the place remains a huge mystery.

The Nightmare Sinkhole was discovered by an expedition team from the Jungle Boss travel company in Quang Binh in 2016. The team returned to the site in 2020.

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The Nightmare Sinkhole is 250m deep. Photo: Jungle Boss

Mr. Le Luu Dung, director of Jungle Boss, said that Nightmare is the only sinkhole in Quang Binh that has only one approach, which is a vertical rope swing at a height of about 250m.

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This is the only sinkhole in Quang Binh with only one access road. Photo: Jungle Boss

"In the early days of exploration, the group encountered many difficulties due to the deep and dangerous terrain of the well. The only way to get out of the hole was to swing back down the rope (other holes in Quang Binh have an exit at the bottom).

The name Nightmare was born from such arduous expeditions that drained the explorers' energy and time," said Mr. Dung.

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According to Mr. Dung, less than 10 people set foot at the bottom of the sinkhole. Photo: Jungle Boss

Because of this difficulty, very few people have ever set foot at the bottom of the Nightmare Pit.

As one of the people who directly climbed down to explore the bottom of the Nightmare sinkhole, Nguyen Van Uy (born in 1988) shared that this sinkhole is located in a valley, to get up one has to cross many sharp cat-ear rocks.

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Moss and vegetation grow lushly all year round. Photo: Van Uy

The mouth of the hole is 66m long and 35m wide. The hole is about 250m deep. The walls of the hole are covered with moss and ferns that grow green all year round. “The bottom of the hole is an underground river with emerald green water, the depth is not yet determined, we swam about 1.2km then the river flows down a cliff.

According to preliminary predictions based on the terrain, the water may flow underground and dive into the nearby Tra Ang cave. Because of this mystery, this will be a destination for those who are passionate about exploration," said Mr. Uy.

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The bottom of the sinkhole is an underground river, the depth of which is unknown. Photo: Van Uy

Currently, this place has a zipline experience service for those who love adventurous sports.

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After swimming about 1.2km, the river flows down a cliff. Photo: Van Uy

However, visitors can only swing across the rope to admire the entire sinkhole from above as well as experience the feeling of floating in the air when looking down to the bottom of the deep hole.

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Photo: Jungle Boss

This is a new type of adventure travel experience in Vietnam.

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Looking up from the bottom of the Nightmare sinkhole. Photo: Jungle Boss

This system is designed with 3 international standard stainless steel cables. Each cable has a load capacity of up to 7 tons. Of which, 2 main sliding cables will be connected to the safety belt through a pulley system, the remaining cable plays a protective role.

All zipline anchor points are arranged independently, calculated according to uniform force angles and equipped with an active braking system.

Phong Nha is among the top beautiful landscapes with great potential. Business Insider magazine (USA) published a list of 100 wonderful tourist destinations in the world, but attracting international visitors is not commensurate with its potential.