When I was young and used to hitch hike and ride bicycle cross country I spent a lot of time under bridges. It is like a free shelter - normal people don't go there - but there is a lot of remnants from teenagers and drifters. I got a good appreciation for the amount of work, care and beauty that goes into building these structures that we just drive back and forth across and pay so little heed to. They are a transition point between here and there - and like dawn or dusk hold a special magic.