When we cruised the Rhône River in France last November, we passed through many locks and canals along the way. Most of the time we sailed at night and so we missed the claustrophobic sensation of squeezing through the locks although I would occasionally awake in the night and open the curtain because there was no light, only to discover a cement wall inches from my nose. I was in the room one day as we passed through a lock during the day time and I could reach out through the open sliding door (it had bars to keep us from falling out) and touch the slimy concrete wall. When I looked up and saw the First Mate seeming to grimace as he monitored our passage through the lock, I stuck my camera out the window, being careful not to lean out too far and scrape against the wall; the wall was so close, it easily could have happened.
If you click on the photograph itself, it will take you to a window where you can view the photo in its entirety to give you a better idea of what I was seeing. I took the photo vertically to emphasize the narrowness of the opening. A sliver of sky is visible at the top and a narrow ribbon of water is visible at the bottom. The metal tubing visible just above the ribbon of water is the barrier that separated me from the wall.