Upper Mustang only introduced to non-Nepalese trekkers 20 years ago, and access is still restricted today. In the 1950s, Tibetan Khampa guerrillas fought back from a stronghold in Upper Mustang. As a result, the Nepalese government has declared the Mustang area an exclusion zone.
However, since 1992, it has accepted many foreign tourists. Trekkers require special trekking permits and must be accompanied by a trekking guide to visit Upper Mustang.