Plan as early as possible as heavy rush is always there in this route. Its tough to get tickets if not booked early. The journey is okay as you get to see lots of greenery on the way - lush green paddy fields, large water bodies, etc. So, I would suggest that it is better to book AC tickets as the daily passengers otherwise will accompany you all the way up to Bardhaman station and they do it regularly, and better not to say anything to them. Outside the NJP station you will have no of options to go to Gangtok which include private taxis, sumo, max or you can go by sharing also. SNT bus will be available but for that you need to go to Siliguri which is 15 minutes from the NJP station.
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