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Longyou Caves is located in Fenghuang Hill of China’s Zhejiang province. It comprises 24 man-made caves constructed in the natural sandstone of the region.
The caves were accidentally discovered in 1992 after the local ponds were drained by the local farmers and five large and 19 smaller caves were revealed.
The five caverns are independent of each other and span over 18 to 34 metres and are 20 metres high. They have supporting pillars and strikingly carved walls and ceilings.
It was earlier believed that the caves were natural as they had distinct designs and formations when compared to other man-made caverns in China.
After further study, it was discovered each cavern had only one portal and a water collection system in the cavern base. The caverns were also designed in an orientation to receive maximum sunlight.
There is a possibility that the cavern was built by carving rocks from top to bottom using chisels of different sizes as several such tools were discovered in one of the large caves.
However, archaeologists and academics are still investigating why, who, and when the caves were created since they were first discovered. Only a Chinese poem by Yu Xun, written in the 17th century, gives some evidence of their origin.
The age of the cavern is expected to be around 2,000 years as archaeologists have found glazed clay pots in the cavern, which dates to the Western Han Dynasty between 206 BC and AD 23.
There are various speculations as to why were they constructed - a mausoleum, secluded military camps, underground storage, ancient quarries, reservoirs, a palace, Taoist dwellings, or a ceremonial place for making offerings to gods and ancestors.
While each possibility could be reasonable, the lack of evidence makes it unable to conclude. The mystery of the Longyou Caves remains until further research gives some clues.