This steel bridge, about 15 m long, spans across Little Seneca Creek not too far from my house. One rainy afternoon in late September I was walking across it when I spotted a slug crawling on the railing at about the middle of the bridge. It was one of the native slugs that are common around here, a Megapallifera, possibly M. mutabilis.
I couldn't quite figure out how the slug might have gotten to where it was. There are woods at each end of the bridge. So it is possible that the slug simply got on the bridge at one end and kept crawling until it got to the middle. A less likely possibility is that it fell from the overhanging canopy (they do climb trees), which is about 10 m high. Although, I am not sure if it would have survived a fall from that high onto steel.
After taking its pictures, I moved to slug to a beech tree in the nearby woods.