The Longyou Caves are a series of large artificial sandstone caverns located at Phoenix Hill, near the village of Shiyan Bacon on the Qu River in Long your County, Quzhou prefecture, Zhejiang province, China. They are thought to date to a period before the creation of the Qin Dynasty in 212 BCE, although no trace of their construction or even their existence has been located in the historical record. First discovered in 1992, 24 caves have been found to date, one of which has been developed as a tourist attraction. The caves are notable in several respects; The caves are very large considering their man-made origin: the average floor area of each cave is over a 1,000 square metres (11,000 sq ft), with heights of up to 30 metres (98 ft), and the total area covered is in excess of 30,000 square metres (320,000 sq ft). The ceiling, wall and pillar surfaces are all finished in the same manner, as a series of parallel bands or courses about 60 cm wide containing parallel chiselling marks set at an angle of about 60° to the axis of the course. Obviously these caves were created by a excavating machine of some sort... though they predate the Qin Dynasty in 212 BCE. They have maintained their structural integrity throughout their existence given modern day excavations probably will collapse within a few hundred years, or so.