The wild abandoned railway in the centre of Paris
25 October 2013 Last updated at 00:15 BST
Long before the Metro, the steam trains of Petite Ceinture ("Little Belt" in English) connected Paris's main railway stations carrying people around the city along the path of its ancient walls. The circular line went into gradual decline from the 1930s, when competition arrived in the form of the more modern underground Metro system.
For 32km (almost 20 miles) the tracks of Petite Ceinture snake through bustling Paris, isolated and largely unseen from street level in deep cuttings, long tunnels, and bridges. Nature has reclaimed the space and it has become a haven for wild flowers and animals.
The line is officially off-limits to the public, but this hasn't stopped many people attempting to explore it.
There is now a fierce debate in the French capital about what to do with the tracks and stations of the Petite Ceinture that still remain. A small section opened as a park in August 2013 and the mayoral elections offer competing plans for cycle routes and parks. Associations set up to preserve the space would prefer to see the line reopened for pedestrian services.
BBC News joined Thomas Jorion - a photographer who has been documenting the line since 1996 - on a tour of what he calls the last great wasteland in Paris.
Video journalist: Neil Meads
Stop/Start is a series of video features for the BBC News website which follows both new trends that are beginning and old traditions that are coming to an end.