The mystery of the ages! Longyou Grottoes is one of the highest level of underground man-made buildings in ancient China. It is also a wonder of the development and utilization of underground space in the world. It is a reflection of the vastness and depth of the Chinese nation. Longyou Grottoes can be traced back to 212 B.C. or even longer, but the age of construction is still unknown. It is the largest ancient underground man-made building ever found in the world. Longyou Grottoes integrates humanities, art, culture and engineering technology. Therefore, in 1992, the world legendary grottoes are Longyou Grottoes, which are displayed in front of people. Not only the age of construction is unknown, but also the causes and uses of these grottoes are different opinions. They have become a mystery that can not be solved for thousands of years. They are also called by local people as the Ninth Wonder of the world-quot; and they are national AAAA-level scenic spots.