By Air: You can catch a direct flight from Nepal through Air China and Sichuan Airlines. To get to Tibet and it is one of the most scenic flights as you will fly over world's highest mountain Everest with the view of many Himalayas as well.
By Road: If you wish to travel by road, there is only one way, through Kerung Port (Rasuwa Port on the Nepal Side).(Missing Subject)To road to Kurung from Kathmandu is mostly unpaved and some parts are so narrow only one car and pass through. During May to October, it is suggested that you check the road conditions at that time the roads are prone to landslide. From the Rasuwa Bridge it is about 24 km to Kurung Town. Since the earthquake in 2015, the Kodari/Zhangmu Nepal-China border has been closed for tourist.
By Railway: One of the best ways to travel to Tibet from Mainland China is by Qinghai-Tibet Railway also known as the rocket to the roof of the world. It takes you 40 hours to reach Tibet.
By Flight: There are plenty of options to get to Tibet via air from mainland China as there are many flights to Tibet even during the off seasons.
You can catch a flight to Lhasa operated from Beijing with Air China, Shenzhen Airlines, Tibet Airlines and Shandong Airlines. Some airlines have transit in Chengdu or Xi'an. You can also take flights operated by China Eastern Airline, Air China, and Tibet Airline that transit at Chengdu or Xi’an from Shanghai; it takes about 7 hours in total.