By Road
Bus is the most convenient option to reach Nepal from India. There are direct buses that operate between Delhi and Kathmandu. Travelling by car is also a common practice. You are required to pay a toll fee and a transport permit at the border crossing. Do not forget to collect the receipts as you might be asked at other checkpoints. Please note, there is a lot of traffic at the border that often makes the journey tedious.
By Train
There are regular passenger and cargo trains that connect Sirsiya (Southern Nepal) and Raxaul (India). There is no visa requirement and this option is only open to Indians and Nepalese. Recently, officials have announced the launch of a direct passenger train between India and Nepal. The train would run from Jayanagar (Bihar) to Kurtha (Dhanusa District, South-eastern Nepal).
By Air
The best way to reach Nepal from Delhi is by flight. There are direct flights operating in this route. These airlines include Indigo, Royal Nepal Airways, Jet Airways and Air India. You might find some great deals if the flight is booked in advance. The approximate travel time is one and a half hours.