The Tribhuvan international airport in Kathmandu is Nepal's only international airport. The important airlines that serve Kathmandu are Indian Airlines, Thai International, Bangladesh Biman, China Southwest Airlines, Druk Air, Air China, Qatar Airways, PIA- Pakistan Airlines, Gulf Air, Sahara Ailrlines, Jet Air, Silk Air, Etihad Airways, etc...
The National Carrier - Nepal Airlines Corporation (NAC) operates two flights per week from London and one from Paris via Dubai. Contact its agency in London for cheap excursion fares. All of NAC's European flights operate via Frankfurt.
Lufthansa also operates direct Frankfurt-Kathmandu flights with three flights weekly throughout the year. German bucket shops can produce special deals on these. Pakistan International, Bangladesh Biman and Aeroflot all have a one- airline service from Europe to Kathmandu, though they require a connection in Karachi or Dhaka or Moscow. From Germany, look at charter flights; LTU operates a weekly flight from Germany to Kathmandu during winter.
You could travel to Kathmandu via Bangkok, Hong Kong and Singapore. There are daily flights to Kathmandu from Bangkok.
If in India, you can fly to Nepal from Delhi, Mumbai, Calcutta, Bangalore and Varanasi. There is the spectacular flight from Lhasa to Kathmandu on Saturdays, Tuesdays and Thursdays operated by Air China. You can also fly Druk Air from Paro in Bhutan, or take a flight from Dhaka, Bangladesh.
From Europe and Middle East
Qatar Airways, Etihad air and Gulf Air operates 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, Austrian Airways has a direct flight from Vienna to Kathmandu and Martin Air operates direct flight to Kathmandu from Amsterdam.
From North America
You could fly to Nepal via India or alternatively via Bangkok or Hong Kong. NAC's Osaka flight makes good connections with North American flights.
From Australia and New Zealand
Look for routes via Singapore, Hong Kong or Bangkok.
There are just eight entry points into Nepal by land open to foreigners, from which six are from India and two from Tibet.
The crossing points from India include Mahendranagar, Dhangadhi and Nepalgunj in the west, Sunali, Birganj 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, there are no tourist buses on either side of the border. You can board direct buses to the Nepal border from Delhi, Varanasi, Calcutta, Patna and Darjeeling. From the border, you can board Nepali buses to Kathmandu.
You can cross the border into Nepal from Tibet via Kodari.
There is no departure tax / airport tax on international flights. On domestic flights including the mountain flights, there is an airport tax of Rs 170 (roughly 2.5 USD).
Custom and duty
Those arriving at Kathmandu airport without any dutiable goods can proceed through the Green channel for quick clearance without a baggage check. If the passengers are carrying dutiable articles they must pass through the Red channel for Customs clearance. Besides their personal belongings, passengers are allowed to bring into Nepal for free - 1 pair of Binoculars, one still camera (with 15 rolls of film), one movie or video camera, a laptop computer, a portable music system, 200 cigarettes or 20 cigars, 1 bottle of liquor and a reasonable amount of perfume.
It is illegal in Nepal to export objects over 100 years old (sacred images, paintings, manuscripts) that are valued for their religious and cultural significance. Tourists are advised not to purchase any item of antique value as they are Nepal's cultural heritage. If you are going to buy such articles you are supposed to certify from The Department of Archaeology at Ramshahpath, Kathmandu for all metal statues, sacred paintings & similar objects before carrying out of the country.
Nepal is 5 hours 45 minutes ahead of GMT and 15 minutes ahead of Indian standard time.