Independent travel is not permitted. Once in Tibet, foreign visitors must be accompanied by a licensed Tibetan guide and travel on a pre-arranged itinerary in a chartered 4x4 or minibus. Almost all tours are organised this way, which also solves the logistics: the distances on the plateau are vast, and the roads outside Lhasa — the Friendship Highway to Nepal, the road to Mount Kailash, the route north to Namtso Lake — all require a high-clearance vehicle and often a driver who knows how to handle the altitude. Within Lhasa itself, walking, taxis and the city bus system are enough to cover the main sights. The railway that runs between Lhasa and Shigatse is the only rail link inside Tibet.