The site, which, archaeologists estimate, dates back to the Northern Wei Dynasty (386-534), shares cultural and artistic consistency with the Mogao Caves. The Dunhuang Academy also oversees the Yulin Caves.

As the mural vividly portrays, some listeners slightly lean forward, thirsty for knowledge. Some are puzzled, some look around. Some whisper to others, while some doze off.

It was Li's most relaxed moment during the interview. He's always been astonished at the ability of the ancient painters to precisely portray the mental state of the characters, and to present dynamic scenes with static images.

"It's a satisfying undertaking rather than a job that I'm obliged to get done. It fills me with joy to think that I have contributed to their survival and inheritance," Li says.

He adds that, as his knowledge accumulates and his understanding toward the artworks deepens, it becomes even more insufferable when his hands cannot keep up with his mind, like a doctor who knows what disease a patient has, but fails to treat it.

In March, he won first prize among mural and painted sculpture restorers at a national vocational skills competition related to cultural relics, which was held in Shanxi province. Nonetheless, there's always the motivation to further improve his skills, he says.