NSA's 'dark tower' in Manhattan

Looming over Lower Manhattan, the Long Lines building has been the subject of speculation and mystery for decades. Its concrete facade bears no windows, and barely any light emanates from this dark tower.

Recently, online journal The Intercept published a bombshell story, based on documents shared by NSA leaker Edward Snowden, saying that the Long Lines building may be one of the NSA's most crucial eavesdropping posts on US soil.

Alex spoke to Stanley Greenberg, a Brooklyn photographer who was able to go inside the skyscraper in 1992. Most of the building is owned and operated by AT&T, operating long-distance switching for telephone calls.

Greenberg photographed what appears to be banks of backup batteries inside the building. The trip inside was part of Greenberg's longtime love of hidden spaces in New York City, and his photographs take audiences behind the scenes of places like the water systems and subways to showcase the invisible New York.