Delhi to Gorakhpur -
/search/664/539From Gorakhpur catch a bus to the Nepalese frontier at Sunauli (Indian side) and Bhairawa (Nepalese side, often also called Sunauli). Journey time about 3 hours.
Walk across the frontier, it's then a few minutes walk to the Bhairawa bus station. Take a bus or jeep on to Kathmandu. Buses take 9 to 12 hours. There are many buses daily, either daytime buses leaving regularly until about 11:00 or overnight buses leaving regularly from about 16:00 until 19:00.