What is the key to the mysterious vault in Beishan?

The key to the mysterious vault in Beishan is in Beishan Hotel. There are six safes in the key room of No.2 leisure room on the third floor of Building C, one safe, the key room of No.4 box on the third floor of Building C, one electronic safe, the secret room next to No.4 box on the third floor of Building C, one safe, the key room of Building D, the key room of Building D, the key room of Building B and the key room of Building B. Then the sewage treatment plant has two safes, one in the key room on the first floor, one on the second floor and one in Beicun.