This is a potentially cool and long-running thread! I've seen a few of these on other boards, too and they can go on for a long while.
My finds (at least ones I remember at the moment):
1.) A burial trench on the Gettysburg battlefield-- in the woods of Culp's Hill where a lot of Confederates were buried in mass graves. Probably soldiers from a Maryland regiment as that monument was not too far away.
2.) I once went on a spiritual retreat at a monastery and took a hike in the woods with a group of monks. We found a weather balloon which we mailed back to the weather scientists. I actually joined that monastery a few years later (yes, I am a monk and priest--love to hunt!).
It just occurred to me that a group of monks running around a forest with a weather balloon might in itself qualify as one of those "strange things found in the woods." LOL!