When we first moved into my house (the house I currently reside in) 20 years ago, I wandered up the attic to stack some boxes. Most of the attic is covered in that white powdery stuff that you're not supposed to walk on, else you'll fall through the floor. The old owners put wooden planks over the beams on one half of the attic so we could walk there and stack storage and everything. The creepy thing is, there were several large footprints in the powder. When I showed my dad, he was just as baffled as I was because again, if anyone stepped over there, they'd have fallen right through. And the footprints were BETWEEN the beams as if whoever was there, stepped over the beams which would've been the only stable parts to walk on.
The footprints are still there 20 years later and it still weirds me out!