Nepal is a landlocked country that lies in between India and China. Being a land locked country, it has no naval ports. So, you can get in Nepal either by land or by air.
Things to be considered before entering Nepal
Tourists can obtain entry visas easily upon Nepal arrival (exception: people from few countries in Africa and Middle East). You need to fill the visa application form and attach 1 passport size photo.
Nepal has only one International Airport named Tribhuvan International Airport. It is located in Katmandu- the capital city of Nepal. No direct flights for Kathmandu is available from European countries. You need to take a transit at Arabian countries like Doha, Abu Dhabi, Dubai and Istanbul) or you can take any other transiting flight to Kathmandu.
If you want to enter Nepal from China by Air, you can take China Kathmandu flight from either Lhasa or Kunming or Guang Zhou. Air China and China Southern Airlines/China Eastern are popular airline companies in China.
Transit point will either be at Hong Kong, Singapore, Bangkok, Kuala Lumpur, Seoul, Istanbul or Delhi if you are willing to take flight from America to Nepal.
If you choose land transportation, entry point for Nepal will be at Tibet (China) and India. These entry points remain open 24hrs a day. Foreigners are not allowed to enter Nepal from spots other than these entry points.
Mauri (at Humla which links Far Western Nepal with Tibet)
Kodari (at Sindhupalchowk which links Nepal with China)
Gadda Chauki/ Mahendranagar (at Kanchanpur which links Far Western Nepal with India)
Mohana (which links Dhangadhi, Kailali and Far Western Nepal with India)
Jamunaha (which links Nepalgunj, Banke and Far Western Nepal with India)
Belahia (which links Bhairahawa, Rupandehi and Western Nepal with India)
Birgunj (which links Parsa and Central Nepal with India)
Kakarvitta (which links Jhapa with Darjeeling/Sikkim of India).
Tourists most popularly use Benares- Belahiya- Lumbini- Pokhara- Kathmandu route from India to Nepal. For Bhutan and Sikkim, you can choose the enry point in Kakarvitta.
By land with private vehicle
You need to require International Driving License and you can drive on roads of Nepal by paying small sum of daily fee. The time period is limited to six months.