The Jade Chamber in Genshin Impact is a floating castle that you need to access as part of the quest The Floating Palace in the third chapter of the first act. You are invited to the palace by a stranger named Ganyu, an emissary of Ningguang, but she doesn't tell you how to get there. Together with Paimon, you'll need to figure it out.
Inside the Jade Chamber, Ningguang will greet you, tell you about the palace and the Archon War, and then invite you inside. In the palace, you can look around, take the scroll Li Yue Tradition: Meeting the God from the table behind Ningguang, talk to the Jade Chamber's secretary Bai Shi to receive the Diligence directive reward. But there's something even more interesting: while the quest is not yet completed, approach the cabinet with scrolls to the right of the wall with papers that Paimon noticed. There, you can take a Strange Notebook with a cipher that needs to be deciphered. It's simple, the cipher is recorded as follows: paragraph: word: letter | letter, and you need to look in the scroll Li Yue Tradition: Meeting the God that you took earlier. The decryption of the note in the notebook:
Once you take the paper with the map from the wall, the quest will be completed, the notebook will become unavailable, and the Equilibrium quest will be accomplished.