Kinda long but worth the read:
I made a tree fort with some friends in the woods that were supposedly "Indian burial grounds (Lenni-Lenape)" when we were 15yo. Once done we decided to camp out. Right around 11pm we ordered pizza and had it delivered to the house just outside of the woods, bout half a mile away, we figured if we waited on the curb we could just pay the guy when he showed up. 2 guys went to the curb, me and my buddy stayed in the treehouse. After 10 minutes of the guys being gone we hear rustling of the leaves from outside like someone dragging their feet in leaves, but its opposite of the trail. We look outside and see nobody, then BOOM! the bottom of the fort lifts up. I'm not talking someone hit it, I'm talking it actually bows up. The same noise happens again, and stops right in front of the fort's door opening. Suddenly the sound runs down the hill and into the creek. (The fort was made right next to a big dropoff that ran down to the water, it was so steep that if we ever dropped a hammer down there it would take 5 minutes to get it back as you'd have to use roots to climb back up) What felt like an eternity went by. Suddenly the sound comes running back up the hill in like 4 seconds, and under the fort, BOOM, BOOM, BOOM, BOOM, BOOM, BOOM!!! Forts bottom gets hit again like 10 times in a row.. Then the sound just walks off deep into the woods. Me and my friend are statues, unable to move. About 1 minutes later my friend and I Puke at the exact same time. When our other friends come back 20 minutes later they right away know something is wrong, theres puke everywhere, we can't move and are white as ghosts, supposedly my buddy looked "demonic" in the dim lighting we had but I don't remember that. We huddled into a group and walked out of the woods terrified.
The next day my friend's parents went into the woods as they thought it was just someone messing with us and they were ready to file a police report. Only problem was.. There were no footprints in the mud under the fort, there were nails everywhere that would have prevented someone from putting their hands on the fort to lift the bottom in the dark, the fort was too tall to really push up on, and too solid to make the floor bow like it did the night before, also the hill was just too steep for someone to run up as quickly as they did.
16 years later I've never stepped foot back into those woods, and I have been terrified by the idea of ghosts ever since and can't sleep in old houses.
I always tell myself it was probably a big white tail deer that was using the bottom of the fort as a rub.. though I know that's unlikely.