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) United Arab Emirates (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, be it from USA, Europe, come to Nepal via connecting flights from the places above.
You can also travel to Nepal by road from India in the south and China in the north. You can travel by train or bus to the Indian border with Nepal and then by road to reach various cities in Nepal. You can travel from Delhi to Banbasa, the border town of India, by bus, which takes about 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 trip from Gorakpur to Sunauli (3 hours). Then you can travel from Bhairahawa, the border town on the Nepalese side to Kathmandu, Pokhara.
You can also travel from Calcutta to Raxaul by train (15 hours). You can also travel from Patna to Raxaul (7 hours) by bus. Then take a bus from Birgunj, the Nepalese border town next to Raxaul, to Kathmandu (10 hours), Pokhara (9 hours). You can travel from Darjeeling to Kathmandu via Kakarbhitta, the border town of Nepal. You must travel from Darjeeling to Siliguri, then from Siliguri to Panitanki (1 hour). Then cross the border to Kakarbhitta and then travel to Kathmandu by bus (14 hours).
You can also travel by road jeep from Lhasa to Kodari, China’s border with Nepal. From Kodari, you can take a bus on a 5-hour drive to Kathmandu, the capital of Nepal.