There is an inaccurate Facebook meme out there identifying this as a "10,000 year old hidden library." It was walled up, apparently, but the New Yorker had a story about it a number of years ago that is a good antidote to the click bait piece.

A Secret Library, Digitally Excavated

Just over a thousand years ago, someone sealed up a chamber in a cave outside the oasis town of Dunhuang, on the edge of the Gobi Desert in western China. The chamber was filled with more than five hundred cubic feet of bundled manuscripts. They sat there, hidden, for the next nine hundred years. When the room, which came to be known as the Dunhuang Library, was finally opened in 1900, it was hailed as one of the great archaeological discoveries of the twentieth century, on par with Tutankhamun’s tomb and the Dead Sea Scrolls.

The library was discovered by accident. In the early Middle Ages, Dunhuang had been a flourishing city-state. It had also long been famous as a center of Buddhist worship; pilgrims travelled great distances to visit its cave shrines, comprised of hundreds of lavishly decorated caverns carved into a cliff on the city’s outskirts. But by the early twentieth century, the town was a backwater, and its caves had fallen into disrepair. Wang Yuanlu, an itinerant Taoist monk, appointed himself their caretaker. One day, he noticed his cigarette smoke wafting toward the back wall of a large cave shrine. Curious, he knocked down the wall, and found a mountain of documents, piled almost ten feet high.

This is the debunking article about the Facebook nonsense.