Introduction to the Underground Xuan Palace: The underground Xuan Palace is located at the northern end of the Shinto central axis. The tomb mound where it is located is also called the Longevity Mountain. About two meters above the ground, there is an east-west corridor in front of the stone gate, 18.8 meters long, connected to the north and south tomb passages in the middle. The three generations of Emperor Zhu Yuanzhang, great-grandfather and grandfather were buried here.