La Petite-Ceinture (PC) is an abandoned, or some prefer to say, disused, railway line that used to circle Paris.
The Petite-Ceinture line circles around Paris, hence the name "Small Belt". It was used for metro-type passenger trains until 1934. Since then, it is completely abandoned, made obsolete by the new underground metro lines, but most of the rails, tunnels and stations still exist. The line mostly runs in trench or overpasses, with a few tunnel segments.
For more informations on this abandoned railway line (in french), check this Wikipedia article and www.petiteceinture.org.
This is a NO TRESPASSING area. Enter at your own risks!