Underground New York
"ew York's subway system, the nation's largest, turns 100 next month - a big moment for an institution we take so much for granted...When it opened in 1904, the first subway line covered just nine miles of track north from City Hall to Harlem, but it had an effect like Columbus's voyage to the New World. New York City was already 240 years old, and most of its population was crowded in Lower Manhattan, unable to venture far from the city's job center. Underground transportation arteries freed the city to grow."
Thanks to Irvin Dawid