This is an impressionist piece! I tried for a long time and on many metro trips to get this right. I used the small camera and gave it a steady resting place against the rear window of the train - then I squeezed the shutter and hoped for the best. There were many failures, but this one seems to have some sense of speed to it - even if the train in the image is braking for he next station! A tunnel is usually associated with a quest and as well as darkness, can involve anguish and punishment. Tunnels frequently appear in dreams, but as usual, the symbol is ambivelant - there may be light at the end of the tunnel. Being in the tunnel is stressful, yet the task of exiting demands thought and consideration. Once when I was in this very tunnel (and near enough this location) I experienced an earthquake, It was unusual for Turin. The train slowed nearly to a standstill and there was a most curious atmosphere. That truly might have become an underworld adventure. In many ancient cultures, there was a belief in an underground highway. The dead and the Sun would travel along the highway and emerge to a new dawn. But in these times, millions of commuters disappear into dark highways under the city every day, In this case they soon return to the familiar world they know. But in the dark Tunnel of the Underworld, one can only emerge to a new place of light, a fresh birth.