The New York City Subway opened for business in 1904. Over a century later, with 472 stops it has the distinction of having the most stations of any subway system in the world. In 2017 commuters made more than 1.72 billion rides on the subway’s 665 miles of passenger tracks. And some of the riders even found time to take a quick nap, like the one pictured here from 1939. Here are 20 of the rarest shots portraying the history of this venerable institution.