The Kingdom of Lo, the traditional Mustang Region and "Upper Mustang" are one and the same, comprising the northern two-thirds of the present-day Nepalese Mustang District. They are well-marked by official "Mustang" border signs just north of Kagbeni – where a police post checks permits for non-Nepalese seeking to enter the region – and at Gyu La (pass) east of Kagbeni.
The Khumbu or Everest region is the most popular trekking area in Nepal. It would probably be the most popular destination, but it is more difficult to get to Solu Khumbu than to the Annapurna area. To get near Everest, you must either walk for 10 days or fly to Lukla, a remote mountain airstrip where flights are notoriously unreliable.