Longyou Caves

Vast chiselled caverns with no record, no soot, no explanation — and identical tool marks throughout.

The Longyou caves (Zhejiang, found 1992): at least 24 large hand-chiseled sandstone caverns, uniform tool marks, no historical record, no soot, estimated million-plus cubic meters removed. Chinese researchers date them speculatively to pre-Qin. The absence of any documentation for a project this size is the anomaly. Links Derinkuyu as the 'undocumented underground engineering' pair.