Mustang is regarded as the last Shangri La on earth. I do not think that I need to add anything more to describe Mustang.
Upper Mustang is a trekking heaven. The mighty Himalayan ranges hide Mustang on their back, making it very hard to get to.
The Upper Mustang was called the Kingdom of Lo for many years. In 2008 the monarchical recognition was stripped by Nepal Government. In fact, Upper Mustang was cut off from the rest of the areas from the 14th century.
The Lobas inhabit most of these areas. Their culture and heritage is similar to neighboring lands of Tibet.
Upper Mustang, being in the rain shadow area, is semi-arid without trees. This means the whole are is very different and incomparable to other regions in Nepal.
If you are a trekker and would love to soak sceneries, then this should be the place, you must visit.