This particular train runs fairly empty. You can easily get tickets and seats as well.
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A walkthrough to getting a seat in 56141.
1) Reach Coonoor Railway station as early as you please (need for reaching early depends on season, I reached at 06:45 in June and was 5th in the queue)
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There'd be a queue near the UTS counter. Sit in the queue.
3) The counter will open at 07:30 sharp.
4) Tender exact change for a hassle free ticketing experience.
5) Tickets for first class are also available at 50 or 60 INR per ticket (don't remember precisely). Ticket in second class costs 10/- INR.
6) Board the train on a first come first serve basis. (It'll be empty anyway so hardly matters).
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Meanwhile you can enjoy steamy sambhar vada available at ONR for breakfast. You'd love it!