Gems in the dark

Caves don't have sunlight and mobile phone signals are nonexistent. It is another world. But nature has done something special down there, with glistening rock deposits giving some caves the majesty of marble skyscrapers. One might also come across fossils of ancient marine life or murals left by cave dwellers thousands of years ago.

In 2013, Zhou embarked on his first official spelunking expedition and made his way to the Niudong cave at the junction of Qingzhen city and Zhijin county, Guizhou.

"The cave was like an alien planet, with its strange and complex geological environment, and I had to feel my way around by climbing and crawling," Zhou recalls.

When he came out, he was covered in mud.

The trip also offered Zhou an opportunity to hone his spelunking skills, such as using a number of tools to move around the cave and taking pictures in the process.

"It's very important to get everything in and out safely," he says, adding that a slip-up might cause a tool to fall on teammates who may be hundreds of meters below him.