To take advantage of these prices you will need to prove you are a leisure traveller, en route to the airport, so you will need to give either your flight details or yr holiday booking reference. I don't think you will need to give this when you arrive at cheltenham-spa station but you may be asked to give them on yr journey from the station to stansted airport.
Going to stansted airport by train is great, you can take a nap, read (even at night), play a game, or just gaze out of the window... The other caveat to buying these inexpensive train tickets from the station to the airport is that there must be at least two adults travelling together. But another great advantage is that children go free. All children under five go free, and then one child over five but under 16 per grown up travelling by train to the airport.
be sure to leave plenty of time to get to stansted airport early enough to eat, shop etc, so check the times of trains from the station before you go. If you end up with time to kill at stansted airport you can always read a book or play a game again! As you have bought your train ticket in advance, you don't need to worry about the opening times of cheltenham-spa station.
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