Due to various reasons some of the trekking destinations of Nepal have not been permitted by Nepal Government. Those sites are known as Restricted Area Trekking. But that does not completely mean you are not allowed to trek in Restricted or Controlled Area. It means that a special trekking permit is required and has to be issued by the Government of Nepal. Once you get that special permit you are able to trek in this area.
Besides natural beauty, Bon Po religion and its traditions including Buddhism are the main features of this area which attracts tourists from all over the world. The Cultural Revolution in 1959 destroyed almost all ancient Tibetan Buddhism in Tibet. Due to this the originality of the religion was lost there. Restricted area of Nepal especially, Upper Mustang and Upper Dolpo share borders with Tibet and they share same ancient Tibetan Buddhism since 8th century. They have no impact of Cultural Revolution and hence it preserved ancient religion. This is the main reason for visiting this place. This area is also regarded as forbidden land. Legends say that Upper Mustang is the place Guru Rinpoche killed devil spirit here chasing the spirit from Tibet.
Some well-known Restricted Trekking areas are: Upper Mustang, Upper Rolwalign, Upper Dolpo, Manaslu Round Trekking and Manaslu Base Camp. The above mentioned trekking sites are located in remote areas of Nepal. It is a challenging trek as the route traverse some tough paths. But this is made up by the fact modern life has had no effect on this part of the country, and the natural beauty is breath taking.