The Upper Mustang Trek is a trek in the Himalayas of Nepal that takes you into the forbidden kingdom of Mustang. The trek is known for its unique landscapes, rich culture and history, and the chance to explore ancient villages and monasteries that have been preserved for centuries. The trek typically takes around 12-16 days to complete and involves crossing high passes, trekking through arid deserts, and visiting the ancient capital city of Lo Manthang. The trek is considered to be moderate to challenging and requires a good level of physical fitness. A special permit is required to trek in this area, and it is recommended to hire a guide or join a guided trekking group