Visitors try a cave via ferrata at the Shuanghe Cave scenic area in Zunyi, Guizhou province. HUANG MEIMEI/FOR CHINA DAILY

Through the dark rims of sink holes and crystalline underground rivers, Guizhou province's karst terrain reveals a landscape carved over millennia. Travelers paddle across glassy, sapphire water and photograph tiered travertine pools and delicate cascades that look like they jumped out of the pages of a fantasy film.

Guizhou is one of China's most karst-dense regions, with about 42,800 cave entrances recorded as of July, according to the provincial natural resources department.

These caves are natural heritage sites and year-round shelters. Their steady cool air makes them ideal for sightseeing and exploration.

Shuanghe Cave in Zunyi, mapped at 437.1 kilometers, is Asia's longest known cave and a magnet for outdoor adventurers. In recent years, the scenic area has shifted toward adventure tourism to meet rising demand. Operators have expanded activities to attract younger visitors and families while protecting fragile cave environments.

Near one cave entrance, a via ferrata consisting of steel pegs and footholds runs along a cliff. Parents and children inch along the safety line, clipping in and steadying themselves.

"My daughter found it challenging last year, so she wanted to try a harder route," said Li Yu, a visitor from Chongqing who returned with her daughter this year to take a more advanced course.

Operators say they're adapting to new tastes. "With rising consumer expectations, the old sightseeing model no longer meets visitors' needs, especially among younger travelers," said Zhang Yifeng, president of the scenic area operator. "We have been working to build experiences that appeal to them."

The site now offers via ferrata lines, 100-meter rappels, cave paddleboarding, and even cliffside coffee.

Zhang said the aim is to attract thrill-seeking 18- to 30-year-olds and families looking for hands-on learning.

Those efforts are paying off. This year's attendance rose 35 percent year-on-year to surpass 620,000 visits by August, with a single-day peak of about 15,000 visitors, the park reported.

Social media is amplifying the trend. About an hour's drive from the provincial capital, Guiyang, Shilong Cave went viral thanks to its photogenic underground river. Locals call it a benchmark water cave. Hashtags on the popular social media platforms Douyin and Xiaohongshu have drawn more than 30 million views and a stream of travel guides and photos.

"Entering the cave felt like disconnecting from the world. It was like stepping into another realm," one visitor posted under photos from a recent trip.

Visitors can boat along the winding underground river, and in summer, some try cave diving or scramble over submerged falls, according to the operator.

Visitors explore Shilong Cave in Qingzhen city of Guizhou by paddleboard. CHINA DAILY

The caverns hold more than 30 terraces, dozens of travertine pools, and numerous fine cascades, local media reported.

Under the lights, crystal-clear pools take on an emerald sheen and transform the dark cavern into a bright spectacle.

"This route is very popular with young travelers. Its appeal is mainly about photo potential and the thrill of discovery," said Zhou Xiao, a team leader and coach with a decade of caving experience.

He said he was stunned by Shilong's scenery when he first entered it in early 2021. "For water caves, Shilong's scenery is world-class. Its relatively low difficulty makes it well-suited to visitor exploration."

The cave operator said that aside from a necessary rivet on a steep slope and a safety rope, no extra fixtures have been added, letting visitors experience the cave in near-pristine form.

But industry insiders warn that cave tourism brings safety and environmental risks. Shilong's operators limit entry and require reservations to ease crowding and shield delicate formations.

"Most caves are undeveloped and routes place heavy demands on guides and team members," Zhou said. He urged visitors not to attempt high-difficulty caves without proper credentials and to join teams led by certified guides.

"With more people taking up caving, cave tourism in Guizhou is heating up, but we're still short on guide certifications and environmental protection awareness," Zhou added. "I have seen some popular caves troubled by litter, so I'm running training courses to help professionalize and regulate the industry."