Want to take a side trip from India to Nepal? It's a popular thing to do and there are a number of ways to go about it, depending on how much money you're prepared to spend. This guide outlines the best options for travel, as well as information about that troublesome two month gap rule on Indian tourist visas.
If you want to fly, Delhi to Kathmandu is the least expensive route by air to Nepal. Otherwise, the best option is to take a train and then a bus.
Many people travel overland from Varanasi to Kathmandu, either by bus, or train and bus combination. It takes less time than overland from Delhi. It's also possible to fly. However, it's much costlier than from Delhi, although it takes around the same time.