The notes that Wu Xie have always carried with him are in this notebook. There are texts, photos, hand-drawn pictures, receipts and vouchers acquired along the way, private evaluations of teammates, and feelings about history. His various thoughts as he traveled to tombs are also recorded in this notebook.
The art and notes about specific tombs visited in the main story was really cool, but there was also some (apparently) purely historical about who fought who and became Duke whatever, which was not as interesting to me. If you know more than basically nothing about Chinese history, it might help you place stuff in the stories in history.