Introduction to Tongxuan Palace: The fourth largest palace is where Master Xuansu lectures. There are a group of immortals attending a meeting in the cave, the Eight Immortals crossing the sea, and all kinds of rare birds and animals with various expressions. Zhuge Liang was practicing in the cave. For three years, I listened to the Heavenly Master preaching here. The Heavenly Master gave Zhuge Liang the three heavenly books "Secret Records of the Three Talents", "Array of War" and "Luxu Xiangxiang" in this palace. There are scenic spots such as the Bodhi Tree, Saha Loess Mountain, and the gathering of immortals.