The sinkhole, a 150-meter-deep natural formation, was created by the collapse of a massive cave ceiling. It is hidden within the UNESCO-recognized Non Nuoc Cao Bang Global Geopark in Cao Bang Province.
According to the Hoa An District Cultural Center, the sinkhole was only discovered and opened for adventure tourism in 2023, after lying dormant in the remote forests of Cao Bang for millions of years.
Pham Van Manh, a 30-year-old from Hai Duong Province, and his friends first explored the area in December 2022. Manh described the sinkhole as a pristine area, untouched by mass tourism.
Manh's discovery of the sinkhole was somewhat accidental. While exploring the Thang Hen Lake area within the Non Nuoc Cao Bang Global Geopark, he heard locals mention a deep area nearby that few had ever reached. Fueled by their passion for adventure, Manh and his group decided to embark on a journey to explore it.
The cold weather in Cao Bang at the time made the expedition challenging. The group trekked 3 kilometers through the forest within the Thang Hen Lake Nature Reserve to reach the sinkhole's entrance.
In February of this year, Manh and his friends returned to the Canh Cao Sinkhole for a more thorough exploration.
The group prepared for their descent into the sinkhole by setting up ropes to secure their safety as they lowered themselves down using abseiling techniques, which involve controlled sliding down a rope.
To stay safe during this process, each person wore specialized equipment, including helmets, harnesses, and ascenders, which help them move up or down the rope safely.
Abseiling is commonly used to navigate cliffs, sinkholes, or caves. For this descent, the group abseiled over 80 meters from the rim to the bottom of the sinkhole.
Upon reaching the bottom, Manh was overwhelmed by the underground cavern, with passages leading to different exits. The bottom of the sinkhole also harbors a primeval forest ecosystem, with ferns and palm-like plants that made Manh feel as though he had stepped back in time.
The sinkhole is part of the limestone mountain system within the geopark and contains several underground caverns, limestone ceilings, and stalactite columns.
As they followed the sunlight filtering into the cavern, the group emerged from the sinkhole just as night was falling.
"It was incredibly satisfying to overcome this personal challenge," Manh said.
For Manh, the experience of abseiling down from the top and hanging in mid-air within the sinkhole was unforgettable.
"It's something everyone should try at least once in their life," he added.
Manh and his group completed their exploration in a single day.
He emphasized that conquering Canh Cao Sinkhole is difficult and full of challenges, suited only for those with experience and knowledge of using safety equipment.
After exploring the sinkhole, the group rested and admired the surrounding landscape.
Manh suggested that visitors could also try paddleboarding on Thang Hen Lake, exploring nearby underground caves, trekking through Ky Rang Cave, and discovering the Eye of God Mountain Valley.
The natural scenery around the sinkhole includes streams and forests, adding to the area's charm.
For those interested in experiencing the Canh Cao Sinkhole, Manh recommended traveling with a large group or joining guided tours for safety. He also advised explorers to train physically before the trip, have experience in trekking, climbing, and using safety gear, and to bring appropriate clothing and trekking shoes.
Since tourism services are not yet developed at the sinkhole, Manh advised visitors to prepare enough food and water for their exploration.
The best time to visit and explore this area is from October to April. Although the valley is surrounded by green grass, the period from May to September is typically rainy, making the roads slippery and potentially dangerous.
