Mystery of the Longyou Caves

Inside the Longyou Grotto caves in China.

The Longyou Grotto Caves in the Yazhou region of China form an extensive, magnificent, and rare ancient underground world. (Image: Zhangzhugang via Wikimedia Commons)

The Mystery of High-Tech Tool Marks in China’s Ancient Longyou Caves

Scientists from around the world wonder how the caves have been able to keep their structural integrity for such a long time. And then there is the question of those tool marks. (By Zhangzhugang via wikimedia)