http://adventure.howstuffworks.com/10-cities-you-can-see-by-mass-transit.htm
One of the best ways to explore a city is via mass transportation. It's an easy and inexpensive way to get around. Above-ground transportation like buses, trams and ferries offers close-up views of local neighborhoods. Subways, trains and light rail let you pass by the traffic jams that often plague the world's big cities, and get you where you're going quickly, leaving you more of that coveted leisure time.
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http://adventure.howstuffworks.com/10-cities-you-can-see-by-mass-transit.htm