The Tribhuwan airport in Kathmandu is Nepal’s only one international airport. The important airliness that serve Kathmandu are Indian Airlines, Thai Airlines, Bangladesh Biman, China Southwest Airlines, Druk Air, Qatar Airways, PIA- Pakistan Airlines, Gulf Air, Sahara Airlines, Jet Air and Cosmic Air
Since it has India on three sides and China on the north, traveling to Nepal by land requires that one pass through either one of these nations. The entry points from India are Biratnagar, Kakkarbhitta, Birgunj,Bhairawa, Nepalgunj, Dhangadi and Mahendra Nagar. The Kodari pass on the Nepal-China boarder is the entry point from China. Tourists entering the erstwhile kingdom by land must possess an international carnet.
You could travel to Kathmandu via Bangkok, Hong Kong and Singapre. There are daily flights to Kathmandu from Bankgkok. If in India, you can fly to Nepal from Delhi, Mumbai, Calcutta, Banglore and Varanasi. There is the spectacular flight from Lhasa to Kathmandu on Saturdays, Tuesdays and Thrusday operated by China Southwest Airlines. You can also fly Druk Air from Paro in Bhutan or take a flight from Dhaka, Bangladesh.
The crossing points from India include Mahendranagar, Dhangadhi and Nepalgunj in the west, Sunauli, Birgunj and Kakarbhitta in the east. Make sure to book your tickets through a reputed agency to avoid getting duped. Also bear in mind that everyone has to change buses at the border whether they book a through ticket or not and that despite claims to the contrary.
The crossing points from Tibet is Tatopani friendship Bridge. There are others crossing points from tibet as Upper Upper Mustang, Dolpo, Simikot and others normally Tatopani friendship bridge is main business crossing points. Its also point to visit Tibet Lhasa, Mt. Kailash exit from Tibet to Nepal. There is also flight to Tibet and Tibet to Kathmandu.
From Europe and Middle East
Qatar Airways and Gulf Air operate daily flights to Kathmandu from Doha and Dubai Pakistan international, Bangladesh Biman and Aeroflot have one-airline service from Europe to Kathmandu. The other option is the charter companies, Austrin Airways has a direct flight from Vienna to Kathmandu and Martin Air operates direct flight to Kathmandu from Aamsterdam.
From North America
You could fly to Nepal via India or alternatively via Bangkok or Hongkong. NAC’s Osaka flight makes good connections with North American flights.