Ancient Carved Caves You Never Heard Of. In June 1992, four farmers in Longyou County, Zhejiang Province, China, decided to settle an old village rumor. Around Shiyan Beicun, on a low hill called Fenghuang Hill beside the Qu River, sat several small ponds. Locals had long called them bottomless. Some held almost no fish. The water just sat there, dark and still, as if it had somewhere else to go. On June 9 they pooled their money, hired diesel pumps, and began draining one pond. For seventeen days the pumps ran day and night. When the water finally dropped, there were no fish thrashing on the mud. There was a stone staircase. Then a doorway. Then a cavern so large the men could barely take it in. They had not drained a pond. They had opened a forgotten underground hall. They kept pumping. Four more ponds gave up four more halls. Later surveys found still more. At least 24 separate man-made caverns now sit in that hill. Some accounts mention additional chambers nearby. The five largest have floor areas of roughly 1,000 square meters or more, spans of 18 to 34 meters, and ceilings rising as high as 20 to 30 meters. Together they enclose more than 30,000 square meters of carved space. They are not connected. Each cave is its own sealed world, even though the walls of neighboring chambers sometimes come within two feet of each other. A short tunnel would have been easy. Whoever cut these rooms chose isolation. The rock is pelitic siltstone of the Cretaceous Quxian Formation, reddish, fine-grained, soft enough to work by hand when freshly cut, then hardening as it weathers. Every surface carries the same signature: parallel chisel courses about 60 centimeters wide, the tool marks set at a consistent 60-degree angle, wrapping walls, sloping roofs, and massive rock pillars like a repeating current. In places the pillars take a fishtail cross-section. In one chamber a relief of a horse, a bird, and a fish still rides the stone. Estimates of the stone removed run near one million cubic meters. No spoil heaps have been found. No tools were left behind. No contemporary chronicle, gazetteer, or imperial record names the project. China kept meticulous accounts of canals, walls, palaces, and tombs. These halls do not appear in them. The only later written echo is a 17th-century poem by Yu Xun. Pottery shards from silt inside one cave date to the Western Han, between 206 BC and 23 AD, so the work is at least two thousand years old. How much older is still argued. Perhaps 1000s of years. Theories pile up and collapse: quarry, tomb, storehouse, military cache, ritual hall, palace of a forgotten court. Each explanation answers one question and fails another. The rooms are too finished for a simple mine, too empty for a tomb, too isolated for an army, too vast for a private shrine. For two millennia the water kept them. Full flooding may be why the thin roofs and slender pillars never failed. Then four farmers wanted fish, and the hill gave up its secret. They are called the Longyou Caves, or the Xiaonanhai Stone Chambers. Five of them are open. The rest still wait under the ponds that hid them, and the oldest question in the hill has not changed: Who cut these rooms, and what were they for?