From NYC: "Inside the City's Ghost Subway System," by Jim O'Grady for the WNYC News Blog

The New York City subway system has 842 miles of track, making it the largest in North America. And there's even more to it than riders see: dozens of tunnels and platforms that were either abandoned or were built but never used. They form a kind of ghost system that reveals how the city's transit ambitions have been both realized and thwarted. (Read more here.)