Final answer:
The Diamond Sutra was re-discovered in the Buddhist caves in Dunhuang in 1900 after being sealed up around the year 1000.
Step-by-step explanation:
The Diamond Sutra, one of the most important texts in Mahayana Buddhism, was said to have been sealed up in the Buddhist caves in Dunhuang around 1000 and was later re-discovered in 1900. This notable recovery occurred when the caves, which had served as a repository for numerous texts and artifacts, were explored and studied. The caves in Dunhuang are renowned for their historical significance and are known to have safeguarded a vast collection of manuscripts and religious texts over the centuries.