Nearly four million people ride the Cairo Metro each day, a network stretching out over 69.8km of track and servicing 57 stations.

BBC: Subway systems by the numbers

Take a ride down the metro line that runs southwestward from the centre of Caracas, and it is easy to see why.

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Versailles is a 20km ride from Paris, but groups like Fat Tire Bike Tours and Bike About Tours begin in downtown Paris with a 10-minute metro ride before embarking on the bike part of the tour.

BBC: Easy breaks from Paris