Oil Creek, Pennsylvania
Sorry for the poor quality image, I've taken better pictures of this place in the past, but for some reason I have no idea where I saved them, so as of now this is the best I can do.
Anyway, this picture was taken in Oil Creek State Park in Pennsylvania. We used to take a hiking trip here every year but it has been a while since I went. Before the rolling hills that make up this beautiful place belonged to the state, they were privately owned by oil entrepreneurs in the late 1800s. I don't remember the exact history of the area but I know at one point one of the main oil drillers in the area was making the equivalent of a million dollars a day (I've read some of the plaques here probably ten times over the years yet can't remember much about them).
There are many historical sites along our approximately 25 mile hike, but the area pictured above is not marked on any map. Found just off the trail is the path of wreckage from the main building and the smaller buildings that used to stand around it. Pictured is the main building. I've gone inside a few times but only for a short while as the entire place feels like its ready to collapse.
As there are no formal markings acknowledging this place's existence, I don't really know the true story behind it. I imagine it was a temporary lodging of some kind as inside were the shelves of a pantry, what looked like a den, and a broken stairway leading to an upstairs area. Not much is left there now except for a smashed wooden table and some beer cans and graffiti.
You can see from the picture where trees have fallen on top of the structures or even grown up through them. Again, this isn't the most expertly taken picture (not by a longshot, actually), but the way nature has reclaimed this structure to a point where mapmakers don't even recognize it as a landmark is just remarkable.