Walking on the Olentangy River Trail to clear my head a little, and when I took a seat under one of the bridges, I noticed something really cool:
The concrete of the underside of the bridge had woodgrain patterns in it. Presumably even the little differences in the surface of the boards were enough for the concrete to imprint, and it's such a captivating visual effect.
This is a bridge support and first time I saw it, I thought it was very intentionally applied patterning or something. But then it maked more sense for that just be the woodgrain on the casing.