You should know about visa, weather, culture, and languages before coming to Nepal

Visa Procedure
Visa on arrival is issued for all tourists at the Tribhuvan International Airport in Kathmandu under the immigration department of Nepal. The procedure is very fast and hustles free. There may be few lines of tourists during the tourist seasons.
If you want an even more comfortable way of getting Nepalese visa then contact Nepali diplomatic missions stationed abroad. If you have obtained a Nepali visa from one of Nepali diplomatic missions then you must use the visa within the six months from the date of issuance.
It means you need to enter Nepal within six months from the date of issue of visa. The total number of days stayed in Nepal is counted from the day you enter Nepal. Usually, it is a tourist visa that allows you to enter Nepal and enjoy sightseeing, trekking, and expeditions in Nepal. However, if you wish to change it, you can. You can change it into multiple visas by applying to the Immigration department.
Nationals of a few countries are required to arrive with visas already obtained. However, in case you arrive at the Kathmandu airport without a visa then also you can apply for the arrival tourist visa. For more detail
Weather
Weather in Nepal is not consistent across the country. It may change from region to region and place to place. Nepal is more of a mountainous region and less is the plain area.
Before you take any risk of going out for trekking, expedition or river rafting, it is essential that you read about the weather forecast which will inform you whether it is safe to move or not. You can depend on your mountain guide also. He will tell you whether it is safer to travel or not.
The different topography of Nepal makes the weather flexible all the time. It may be raining in one place and can be dry in another place.
Culture

Nepal is a multi-ethnic country with at least 125 ethnic communities living harmoniously in one society. The different communities have different cultures of different social values.
Some of the cultures may require you to cover up your whole body because moving with fewer clothes on the body is considered strange.
You should be careful not to openly kiss your girlfriend in front of the public because in the culture of that particular place it may be considered a bad human behavior. I may also require you not to openly hug someone you love because it is also considered bad.
Language

Language is a big barrier. So, knowing at least basic knowledge of Nepali language would suffice you to survive in the Nepali remote villages in case you are lost while traveling within Nepal.
Most of the villagers do not speak and understand English as yet. Very few people can speak and understand English.
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