Mustang was opened to non-Nepali trekkers only some fifteen years ago and even today, access is still highly restricted. To enter Upper Mustang, that is to travel further north from Kagbeni, trekkers need special trekking permit and must be accompanied by a government appointed officer.
Upper Mustang, being in the Himalayan rain shadow, is one of the regions in the country suitable for trekking even during monsoons. During this time, the upper Kali Gandaki valley is still quite dry with only occasional rainfall.
The settlements are scattered and there is little sign of cultivation between villages. In upper mustang, little grows without irrigation, thus the region resembles a desert albeit mountainous, nuclear settlements in fertile areas.
Lo Manthang, the old capital, is reached in four days and at least one extra day should be spent here to catch the sights and sound of this unique walled settlement. Ponies are available for hire if you so desire. The return trip can either follow the same route while entering or, as an alternative route, the eastern bank of the Kali Gandaki may be followed.