Autumn (September – November) and Spring ( March – May) is typically regarded as best seasons to travel Nepal for Trekking and Mountaineering. From September through December, there is a pleasant climate neither too hot or too cold. At that season, the mountain’s visibility is more clear. Spring is another excellent time to go trekking and mountaineering in the Himalayas because the sun is warmer. In Nepal, spring is when a wide variety of flowers blossom on both trees and the ground. This is also the ideal season for climbing and expeditions. You can have an experience of a lifetime at that moment.
Having said that Nepal is not just limited to trekking and mountaineering, you can go for more adventure activity such as Bungee jumping, Rafting, Cycling, Canoeing, paragliding, Jungle safari and many more. Similarly, you can also tour around Pokhara, Lumbini, Chitwan, Bandipur. So varying upon your activity to do, through out year Nepal is best to visit.