Well if you haven't looked for it, I would suggest going and finding the lawn mower tree (its about halfway between Pioneer Hall and the Boat Dock). Story goes that someone left a mower there and the tree grew up around it. No idea if its true though.
You also might be interested in one of the nature trails that not many people travel (probably cause they don't know about it). It starts right behind the main general store on the right hand side and can take you a bit into the forest behind Bay lake.
You probably already know this, but at one time Ft. Wilderness had a railroad and some of the tracks are still around. If you're feeling adventurous you can go explore the campground and see if you find some of the old rails. I know there used to be some by one of the playgrounds but that was quite a few years ago.
That's all the info I can think of right now.