There is only one international airport, Tribhuvan International Airport and it has direct flights to and from the following countries: 1) Singapore (Silk Air) 2) Korea (Korean Air) 3) UAE (Nepal Airlines, Etihad Airways) 5) India (Nepal Airlines, Jet Airways, Jet Lite, Indian Airlines, Druk Air) 6) China (Air China, China Southern Airlines) 7) Thailand (Nepal Airlines, Thai Airways) 8) Bangladesh (Biman Airlines, GMG Airlines) 9) Pakistan (Pakistan International Airlines) 10) Bhutan (Druk Air) 11) Bahrain (Gulf Air) 12) Malaysia (Nepal Airlines) 13) Qatar (Qatar Airways) . Basically travelers from all over the world, may it be USA, Europe come to Nepal through connecting flights from the above places.
You can also travel to Nepal via road from India in the south, and China in the north. You could travel by train or bus to India’s border with Nepal and then by road to reach various cities in Nepal. You can travel from Delhi to Banbasa, the border village in India, by bus which takes around 8 hours. Then take a bus from Mahendranagar to Kathmandu which takes another 15 hours. Alternatively, you can travel by train to Gorakhpur from Delhi (16 hours) and then take a bus ride from Gorakpur to Sunauli (3 hours). Then you can travel from Bhairahawa, the border town in Nepal’s side to Kathmandu, Pokhara.
You can also travel from Kolkata to Raxaul in train (15 hours). You can also travel from Patna to Raxaul (7 hours) in bus. Then take a bus from Birgunj, the Nepali border town next to Raxaul, to Kathmandu (10 hours), Pokhara (9 hours). You can travel from Darjeeling to Kathmandu via Kakarbhitta, the border town in Nepal. You need to travel from Darjeeling to Siliguri, then from Siliguri to Panitanki (1 hour). Then cross the border to Kakarbhitta and then travel to Kathmandu in a bus (14 hours).
You can also travel on a jeep by road from Lhasa to Kodari, China’s border with Nepal. From Kodari, you could catch a bus on a 5 hour journey down to Kathmandu, Nepal’s capital city.