The small and isolated Trans-Himalayan "kingdom" of Mustang occupies just over 3,000 square kilometres with an average altitude of 1,000 metres, just below the Photu La pass (1,600m), which is itself only 75m above the Tsangpo plain of Tibet. In all respects, geographically, climatically and culturally, it belongs to Tibet. Today it is part of Nepal but retains a degree of autonomy. The Thak Khola/Kali Gandaki River originates here and flows out of the Mustang valley in a series of deep gorges. It has been vividly described by the French anthropologist Michel Peissel in his book "Mustang: The Lost Kingdom". Entry into this area is partially restricted by the Nepalese Government.

Mustang was closed to foreigners until the Nepalese government allowed the first trekkers into to the area in 1992. Hidden behind the himalayan giants of Dhaulagiri and Annapurna nestling on the Tibetan border, this area offers a rare insight into the Tibetan culture of a region still restricted to only a few trekking groups each year.