Cave explorers face other risks including falls, hypothermia and floods.

"Human beings have an inherent fear of darkness. You can become very nervous when you don't know your next step or whether danger is at hand. Because of that, your stamina depletes fast and you feel exhausted easily," he says.

The fact that every team member generally carries baggage of more than 50 kg also makes the expedition difficult and exhausting.

Inside the baggage is equipment, and food for oneself and food for the team. Yang says most people also carry "emergency food". In his case, he carries candies and chocolate.

"We share our food most of the time. But, we've this rule not to share our 'emergency food' that is reserved for yourself," he says.

Apart from food, the other most important thing when they are in a cave is light.

"It is pitch dark in the cave. If you do not have light sources, you will never get out," he warns.

Yang also stresses teamwork, saying that it is the key to conquering problems and ensuring each other's safety.

"Everyone's life is attached to that same rope and we must be responsible for each other," he says.

"There is no democracy inside the cave. If the captain asks you to do something, just do it. You need to trust the captain and place the interest of the team above self."

What attracts these cave explorers?

For Yang, it is the beauty of stalagmites inside the caverns.

"There were times when I simply couldn't take my eyes off the beauty inside the caves. You don't see such awesome sights outside the caves."

The ecology inside the cave is so fragile that environmental protection is crucial.

"If you touch a stone that is just coming into shape, you might stunt its growth. The same goes for other landscapes inside. It is our rule never to touch anything," he says.

"We try not to leave anything behind except our footsteps. We even collect our waste in bottles to ensure no breeding of microorganisms," he adds.

Yang's caving team has more than a dozen regular members. "Some have almost turned into full timers as they dive deeper into the sport and become more involved," Yang says.

Liu Jia, a company clerk who is also an enthusiast in mountaineering and rafting, says caving is different from other sports because there is no precedent.

Liu got lost in her first caving activity in 2004 but that did not stop her. "The excitement about caving is you don't know what lies ahead," she says.

For Yang, caving is more of a personal curiosity and he has been using it primarily as a pastime, but he says he gains much more from it.

The experience he has gained through years of caving earns him a sense of achievement when he shares his experience with firefighters and university students through training, and when it comes to helping people in dry areas to search for water and authorities to map the roads.

Contact the writer at xuwei@chinadaily.com.cn.