Beneath New York City lies a vast network of abandoned tunnels, caverns, nooks and crannies that the average joe will never see. But urban explorer Steve Duncan is not your average joe! As you'll see in their Undercity series, he and filmmaker Andrew Wonder really like getting dirty below grade. This week they explore a series of tunnels quite familiar to graffiti fans and Manhattan kids with a penchent for exploration: The Amtrak "Freedom Tunnel" underneath the West Side.

Built by Robert Moses in the 1930s, the Amtrak Tunnels on the West Side were meant to allow for increased parking spaces for Upper West Siders (hello, expanded Riverside Park and the Henry Hudson Parkway!). But soon after they were finished they were pretty much abandoned, only going back into service in 1991 as part of the Amtrak Empire Connection. As far as the story goes, the northern part of the tunnels got their "Freedom" name from graffiti artist Chris "Freedom" Pape who used the walls for some of his more notable work (others say the name is a reference to the former shantytowns of "mole people" that used to live down there).

Though the tunnels are still popular with artists, they've been having a much harder time down there since the trains started running again. Recently Amtrak began buffing large chunks of art off the walls. And, as you can see in this video, new concrete walls have been put up in front of some of the natural stone walls.

Unlike a lot of the other places the Undercity guys have gone (sewers, abandoned subways), the Freedom Tunnel is actually not that hard to break into—even, as you can see, in the daytime. Which means there is a lot of interesting footage of it out there for you armchair spelunkers. Here, for instance, is a pretty look at some of the work in the tunnels a bit further north:

Meanwhile, Undercity has more photos from inside the tunnel here and here.