In my old neighborhood there used to be a pretty huge silo (https://www.flickr.com/photos/becca3k/8184742558) <- that is the actual silo, and the inside was hollow, you could walk through it, no doors. It was basically just there for looks, and the residents would take walks around it and such. My friend and I at the time were pretty young and dumb, and the two sides of the inside of the silo were padlocked shut- with pretty rusty hinges and all- and we had been experimenting with lock picking with Bobby pins, and these locks were really bad, not checked on, etc. Anyways, I can't quite remember if we lock picked it or if we got there one day and the lock was unlocked, but one of the doors on the side of the wall that was always locked shut was slightly ajar. Curiosity getting the better of us, we decided to open it and see what was inside. Keep in mind this silo is made out of brick and wood and metal, and it's made out of the type of brick that air can go through. It's really old, the only old building persevered(ish) in the area. So we open the door, and peek inside. It's pretty hard to see, extremely dark and we didn't have any flashlights, but when you step into it- (it was off the ground) there was a very impressively tall and steep flight of stairs leading directly to the top. The stairs are covered in grime and (pellets?) and such that I couldn't really make out, and we being the dumb kids we were decided to climb up the stairs and check it out. It's a pretty long climb, and when we got to the top, it was amazing. I don't remember it very well but the stairs led to a sort of circular platform at the top where you could look down and see all the metal and it looked like there was tons of corn seeds or something. All of it was rusted, but it was still impressive and everything else around it including the roof was pretty impressively shaped wood. I can't really describe it well, sorry. So we take our time, looking around in awe, then all of the sudden we hear this loud "SCREE SCREE" or something like that- I don't remember it well enough to give a great accurate description, but it was definitely coming from somewhere inside with us- and it was almost pitch black, we could only see from the holes in the brick- and we immediately looked at each other in terror, ran back, and flew down the stairs. I mean, flew. I was tripping down all of the stairs. Anyone seen spirited away? I was like chihiro flying down the stairs. We went back a few days later but it was locked with a new lock that couldn't be lock picked very easily.