There is nothing as intriguing as an abandoned tunnel under New York City, and there are plenty of them—subway tunnels, pedestrian tunnels, tunnels possibly holding FDR's old train car. The tunnels hold secrets, or that's what you hope for when you stumble onto one, and the latest under the spotlight has a past and a future...

Mike Murphy at Quartz did some digging when he saw the new Second Avenue Subway line would be shifting the Q train into a previously unknown half-mile loop under Central Park.

One of the Transit Museum's maps that shows the tunnel in the 1990s

The tunnel was built in the 1970s, and runs between the 57th Street and 7th Avenue, and Lexington Avenue and 63rd Street in Manhattan, according to Murphy, who with the help of the Transit Museum was able to present two 1990s-era maps that included it.

Halley Choiniere, an archivist at the museum... found just two periods, of about six months each, in the summer of 1995 and the winter of 1998, where the tunnel appeared on the map. In 1995, the mysterious tunnel was included on the map when the Manhattan bridge was out of service, allowing Q trains to cross back over to Long Island farther up the East River while the bridge was being worked on... In 1998, the tunnel reappeared as a special temporary shuttle service while work was being done on the Sixth Avenue line, cutting off access to lower Astoria through the regular route.

We found an article in the NY Times' archives regarding the beginning of the project—on March 26th, 1971, they reported that "work on the park segment of the project would begin the week of July 4th. The plans fall for two open trenches curving northeast into the park from Central Park South. One, 1,000 feet long, is to start at Seventh Avenue; the other, about 400 feet long, is to start at the Avenue of the Americas. The rest of the tunnels will be dug underground under the zoo and east under 63rd Street."

At the time, the project was expected to go over budget and cost about $37 million, it also cost THE LIVES OF TREES—in a piece from 1977, the Times reported: "Exactly six years ago the New York City Transit Authority started building a subway line under Central Park and since then an acre of trees and grass has been dug up." At least it's finally going to be used again, over 40 years later.