Introduction to Longxian Palace: Located in the Longquansigou in the middle of Dongguan Village, Erdu, separated by a ridge from Xianqi Cave, it was formed 70 million years ago. The entrance of the cave is 510 meters above sea level. The outer layer of the cave is surrounded by mountains. The peaks are abrupt, the landscapes inside the cave are numerous and concentrated, and the wonders and scenery are endlessly beautiful. The hall in the Longxian Palace Cave is 150 meters high, 140 meters wide, 170 meters long, and covers an area of ​​10,000 square meters. Its width is the largest in North China, and it is called the No. 1 Hall in the North.