When people think of the New York City underground, they usually think of the vast subway system, the sewers, or the water tunnels buried deep in the bedrock. Far lesser known are the city’s obscure tunnels that often run from building to building, or through lesser documented parts of the city. Here’s a peek at 7 such locations that will make you question what other hidden subterranean passageways sit beneath your feet.

7. The Farley-Morgan Postal Tunnel

The Farley-Morgan tunnel under 9th avenue
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 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 arrive on Amtrak trains. Amtrak even had a special ‘mail only’ train for a few years, running along the northeast corridor.

The train 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 and the lookout gallery, which was once used as the location for a Storefront for Art and Architecture installation. On a regular visit, don’t miss the Museum of Postal History, which contains a fun vintage collection of mail paraphernalia from the United States and other countries.