Challenge #4 - Olivier

Hi guys :)

Sorry again that I didn't post anything on the previous challenge...

To compensate, here is my participation to Fernando's challenge already !

This has been taken in a tunnel of an old parisian railway called "la petite ceinture". It was used before the subway was built in the early twenties, from 1862 to 1934, circling around Paris at that time. A large part of the railway is still present, and quite easy to access when you know the entrance points :)