Tribhuvan International Airport at Kathmandu is the only international airport in Nepal. There are a number of International Airlines with direct non-stop flights from the Middle East and Asia to Kathmandu. People interested in visiting Nepal from Europe or America have to adjust their flight to Dubai, Doha, Hong Kong, Singapore, Malaysia, Bankok, Delhi, Mumbai , Culcutta, Banglore Dhaka, or Shanghai.
You can enter Nepal overland both Tibet and India. If you are in Tibet, you can enter Nepal by crossing the border at Kodari and then take a bus to Kathmandu. This will take you 7 to 10 hours depending on the road conditions. The easiest and hassle free overland route to Nepal from Gorakhpur, India is via Sunauli/Belahiya border post using train up to border post. The only direct buses from this route to Kathmandu run at night and take approximately 9 hours. Raxaul/Birgung border post can also be used to visit Nepal. But this may not leave you with a pleasant travelling experience. If you are in Darjeeling you can come to Nepal via Karkabhitta. There are also several border crossings in west Nepal.
For travelling around the country, there is good domestic air network and helicopter charter services as well as deluxe tourist coaches. You can also hire private vehicles. Icicles Adventure can help you with all domestic air tickets booking, tourist coaches booking, and organizing private vehicles.