The other two are the Tibet Public Security Permit (PSB) and the Military Permit, which must be obtained if you intend to visit military-sensitive areas. The military permit is issued by the Military Office in Lhasa. It is strictly required for travel to Ngari, Nyingchi, and Nagqu prefectures, which are classified as military sensitive areas. https://theexploretibet.blogspot.com/2025/09/planning-trip-to-tibet-dont-miss-these.html