After the 14th century the grottoes were abandoned and eventually forgotten. In 1900 they were accidentally discovered by a Taoist monk, Wang Yuan, who stumbled upon what appeared to the former monastery library with its collection of scrolls, documents, embroideries and paintings that had been left behind by the Buddhist monks. Bricked up to prevent the contents falling into the hands of invaders, the dry desert air had preserved the paper and artworks.
 
Passing through the area in 1907, the British explorer Sir Aurel Stein heard a rumor of the hoard, tracked down the monk and was allowed to inspect the contents of the cave. It was an archaeological goldmine mainly of Buddhist texts in Chinese, Tibetan and many other Central Asian languages, some known and some long forgotten. There were paintings on silk and linen and what may be the oldest printed book in existence dating to 868 AD.
 
The discovery of the hidden "sutra cave" was a tremendous and startling event for both Chinese and foreign scholars around the world. It attracted extreme attention and as a result was quickly plundered by the rapacious scholars from England, France, America, Russia, and Japan.
 
The sacking of the Dunhuang grottos began in earnest. Stein convinced Wang to part with a large section of the library in return for a donation towards the restoration of some of the grottoes. Stein carted away 24 packing cases of manuscripts and five cases of paintings, embroideries and art relics, all of which were deposited in the British Museum.

The following year a French explorer, Pelliot, passed through Dunhuang and bought more of the manuscripts from the monk. He was followed by others from the United States, Japan and Russia who all carted off their booty. News of the find filtered through to Beijing and the imperial court ordered the remainder of the collection to be transported to the capital. Many were pilfered whilst they sat in the Dunhuang government offices, and Stein reported in 1914 when he returned to the area that find Buddhist manuscripts were brought to him for sale. He also said that Wang had regretted not taking up his original offer of parting with the collection en bloc. For the Chinese it's another example of the plundering of the country by foreigners in the 19th and the early 20th centuries!
 
The Grotto 16 at Dunhuang is the one that attracted global attention and brought treasure seekers from the West. Two Song-dynasty paintings on its walls show Bodhisattvas on a journey. This is the latest evidence of use of the cave and from this it can be surmised that around the beginning of the eleventh century, when the Western Xia people invaded this area and conquered Dunhuang, monks at the Mogao Grottoes prepared to flee. They sealed the cave and never returned. For nine hundred years, the room was silently shut off from the world.

In the year 1900, when the passageway was being cleaned of debris, this stone archive full of sutras, books, embroideries and sculpture was suddenly discovered. It had some 50,000 items in it and these were later found to include not only a large number of Buddhist sutras, but also Daoist works and works of the Confucian canon, in addition to historical records, poetry, literature, information on geography, population, business accounts, calendars and so on. It was discovered to be a full library containing material that documented some ten dynasties, from the Jin in the 4th century to the Song dynasty.
 
The Mogao Grottos form a system of 492 temples 25 km southeast of Dunhuang in a river valley between the Sanwei and Mingsha Mountains, an oasis strategically located at a religious and cultural crossroads on the Silk Road, in Gansu Province. The desert cliffs are completely exposed to the elements and the interiors of the grottos have been severely damaged by wind and water erosion and many have collapsed. Grotto 94 for example, is totally decimated. Today, 492 grottoes are still standing. The grottoes honeycomb a 1600 meters long cliff face which sits on a north-south axis. Altogether they contain over 2000 statues and over 45,000 separate murals. Cave 17 is where Wang discovered the hoard of manuscripts and artworks.
 
In 1961 the Dang River was diverted north of the grottoes to prevent further damage through flooding. Two years later the Tang and Song pavilions at the grottos were rebuilt and the exterior walls of the caves were reinforced with concrete colonnades and blocks. Windows, walls, and doors were constructed to prevent further erosion from wind and drifting sand, and foundations were laid under many of the statues. Walkways were erected on the cliff face to allow access to all the caves.
 
Most of the Dunhuang art dates from the Northern and Western Wei, the Northern Zhou, the Sui and the Tang Dynasties, though examples from the Five Dynasties, Northern Song, Western Xia and the Yuan can also be found. The Northern Wei, the Western Wei and Northern Zhou, and the Tang grottos are in the best state of preservation.
 
Many of the grottos are rectangular or square-shaped with recessed, decorated ceiling. The focal point of each is the group of brightly-painted statues representing Buddha and the bodhisattvas or Buddha's disciples. Because the sandstone here was too soft for fine carving the smaller statues are made of terracotta, coated with a sort of plaster surface and painted with mineral pigments. As with the grottos constructed later at Datong and Luoyang, religious stories and tales from Chinese mythology, and the walls of the caves are painted in intricate detail.

Travel Tips:
If the you do not go with an experience tour guide of groups, you are supposed to pay at least one hour visit to Dunhuang Grotto Art Protection, Examination and Exhibition Center for informative study befor enter the Mogao caves.

Reviews from trip advisor:
Cultural wonder of the world worth the expense of flying to Dunhuang!
These grottos with their Buddhist frescoes are a true world treasure. They are set into a stoney hillside above a small river and while some work has been done to improve access ( including lovely tree planting) you get the feeling they are as they have always been.
The art work is extraordinary and gorgeous and lovingly preserved through efforts of many. The colours are so fresh you feel as if they are recent. We loved our visit with a fantastic guide whose enthusiasm made the experience very special. Go there now..these are very very special!

Art is better than Cappadocia caves in Turke! - The art painted on the walls of the caves is in an amazing state of preservation, although the highly structured access and tour, and total prohibition on even taking photos of the exterior face of the mountain detracted somewhat. The adjacent museum is excellent, and the grottoes in the museum are outstanding reproductions of the originals you just visited ... and you can take photos of them!