This documentary is the shit. Rent the DVD and watch the "making of" featurette - the process of making the film is just as incredible as the film itself
We used to sneak into these very tunnels in college and shoot our student films. There are these air vents every 100 ft or so and where the light comes in and hits the wall there are amazing graphitti recreations of classic art down there. The Mona Lisa in re-created in spraypaint on a wall of the abandoned Amtrak tunnels under Riverside park.