Just a few meters from Parc Montsouris, in the heart of Paris, a 901-meter tunnel has remained sealed for decades... while the rest of the surrounding network has been transformed into pedestrian walkways.

Built in 1864 by the engineer Jean-Charles Alphand, this tunnel was part of the Petite Ceinture, the old railway line that encircled Paris. After a collapse in 1886, a golden age fueled by the World's Fairs, and then a gradual decline in the face of the metro, the line closed permanently in 1934. Today, while other sections have been reopened to the public in several arrondissements, the Montsouris tunnel remains closed due to a lack of funding to secure its tunnel.

This video retraces the history of this forgotten structure in the very heart of the capital.

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