No harm in driving such a long distance,but it should be done in two days.I am from Patna working in State Govt.I too had visited Calcuuta which is more than 800kms away from here in a days time by Maruti800.It was a tieresome journey.After a gap of a day I had to return back too with same car n I had been the lone person who knew driving among persons sitting.So I will advise that make your journey a pleasant one.Both of you are going to njy at Nainital.So drive steadly without taking time preassure on your mind.Then both of you can njy the journey too.
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If he has been driving for more than a couple of years, no harm going for the trip with a bit of adventure. Otherwise, hire a driver. Swift is a good car to take you anywhere. 500 km. is nothing for it.