When people think of the New York City underground, they usually think of the vast subway system, or maybe the sewers, and water tunnels buried deep in the bedrock. Far lesser known are the obscure tunnels – often running from building to building, or through lesser documented parts of the city. Here’s a very unique look at 7 such locations that will make you question where else there might be hidden in subterranean passageways.

7. The Farley-Morgan Postal Tunnel

The Farley-Morgan tunnel under 9th avenue

One of the least known tunnels in New York City is the postal tunnel that runs under the east side of 9th avenue between the Morgan (mail) sorting facility and the basement of the James A. Farley post office. This heavily secured road tunnel was used to move mail to and from a special ‘secret’ platform at Penn Station, where letters and packages would be transported on Amtrak trains. Amtrak even had a special ‘mail only’ train for a few years, running along the northeast corridor.

They stopped hauling mail in the early 2000s, and the stairs and elevators to the platform were sealed shut. In the post office on special occasions you can still experience the loading area (as we visited during Fashion Week) and the lookout gallery, used for a Storefront for Art and Architecture installation. On a regular visit, don’t miss the quirky Museum of Postal History.