A near-impossible descent into the depths of ‘Nightmare’

Located within the Hung Thoong cave system in Phong Nha-Ke Bang National Park, the ‘Nightmare’ sinkhole remains one of the most challenging natural formations in Vietnam.

Since its discovery in 2016 by Jungle Boss, a local adventure tour company, only a handful of explorers have ever reached its bottom.

Measuring 66 meters long and 35 meters wide, the sinkhole plunges to a depth of 250 meters. Unlike other sinkholes in Quang Binh that have exits at the bottom, ‘Nightmare’ offers only one way in and out - rappelling down and climbing back up. This vertical descent makes exploration an extreme challenge, requiring advanced technical skills and significant physical endurance.

According to Le Luu Dung, director of Jungle Boss, early expeditions into the sinkhole were grueling, requiring climbers to navigate a sheer drop with no secondary exits. "In the first expeditions, our team faced immense difficulties due to the vertical descent into an abyss.

The only way out was to climb back up, which was physically and mentally exhausting," Dung explained. The challenging conditions gave rise to the sinkhole’s ominous name: ‘Nightmare.’

An underground world still full of mysteries

Among the few who have successfully descended into the sinkhole is explorer Nguyen Van Uy. He described the journey as one of the most physically demanding experiences of his life.

The sinkhole is nestled within a valley, requiring trekkers to navigate jagged limestone formations before reaching the descent point.

The walls of the sinkhole are covered in lush moss and ferns, thriving in the perpetual humidity. At the bottom, an underground river with striking emerald-green water flows through, but its true depth remains unknown.

Uy and his team swam 1.2 kilometers along the subterranean waterway before reaching a sheer rock face, leading them to speculate that the river might connect to Tra Ang Cave.

"This place remains a mystery, making it an exciting destination for true explorers," Uy remarked.

Extreme adventure tourism: A glimpse from above

While only elite adventurers have reached the bottom, tourists can now experience ‘Nightmare’ in a safer way. Jungle Boss has introduced a zipline tour that allows visitors to glide over the sinkhole, offering breathtaking aerial views of the cavernous pit below.

The zipline system consists of three stainless steel cables, each capable of supporting up to seven tons. Two main cables are used for the ride, while a third serves as a backup safety line.

The structure follows international safety standards, with independent anchor points and an active braking system.

Though adventurers cannot descend into the abyss itself, the zipline experience offers a thrilling opportunity to witness one of Vietnam’s most mysterious geological wonders from above.

Hai Sam