Only Indian nationals can enter Nepal without a visa. Everyone else needs to buy a tourist visa, which can be obtained either in advance from a Nepal consulate or upon arrival. You will need one passport photo and the visa fee in cash, preferably in US dollars.
Single-entry visas are good for a stay of 60 days and cost US$30. Multiple entry visas can be bought for US$80. Visitors can extend their visa for a maximum of 150 days, with each 30-day extension costing US$30. These extensions can be obtained at immigration offices in Kathmandu and Pokhara.
Most of Nepal’s popular trekking areas require separate permits, which can be bought in Kathmandu or through trekking companies. If you get caught in a park without a permit, you will be heavily fined.