Those are swallow nests under a bridge! That little blur on the left side is a swallow in action. Those little dudes are super fast. Don't stand directly under the nests taking photos unless you want an unpleasant surprise from above. Yep. I got pooped on by a swallow.
Well, I don't know about you but I can't think of a better way to end a blog post. Especially one that's named after swallows.