Okay, I'll share a very short version of a story. I've lived in two haunted houses. The one I grew up in was pretty benign. Just things moving around, and sometimes we'd see a little girl, but none of it was scary.
Then as an adult, I stayed with a friend for a few weeks, and that place was terrifying. We called whatever was there a demon, though I don't know that it actually was. It was without a doubt, however, malicious. I won't go into the long version or all the things that happened, but I'll give a couple of interesting tidbits.
First off, my friend didn't tell me that the house was haunted. I figured that out on my own my first weekend there when he was out. I had a telescope and had wanted to go out and test it out as we lived out in the middle of nowhere and had a great night sky. As soon as I stepped outside, I was overwhelmed with a feeling that someone was out there and wanted to hurt me. It's hard to describe because there was nothing to really account for it. No weird noises, I didn't see anything, just this feeling that something was very, very wrong. I rushed back inside, pulled the curtains shut, locked the door, and sat convinced someone was about to come through the door and murder me.
It was pretty irrational, and I probably would have written it off as my imagination, but when my friend got back I mentioned to him that I'd had the weirdest thing happen, and told him about the experience. His response? "Oh...I was hoping you wouldn't notice."
After that he told me all of the strange things that had happened to him, his neighbors, and his friends. Apparently he hadn't wanted to scare me away before I came. I'd lived in a haunted house before, though, so I figured I could handle it.
Now, I won't go into all the details about how weird this is, but I will mention the scariest thing that happened to me while I was there. This strange ghost/demon thing didn't usually do too much, just gave us creepy feelings when we went out at night, and the cat would often circle the room, staring at the walls as if she could see outside and was following something as it paced outside the house. For awhile we thought this thing couldn't get in because most of that awful, creepy feeling (and people seeing the ghost) happened outside. As such, we didn't go out much at night unless we had to. Honestly, we also blocked all the windows because just seeing out at night was creepy as hell, but that's beside the point.
After awhile, strange things started happening in the house. Things would move around while we were gone, we'd hear noises, get that creepy feeling even when the windows were all blocked. It got to the point where we stayed up until the sun rose because we were too afraid to sleep. My friend's girlfriend and I were convinced this thing was able to come in the house and that it was toying with us.
One night, my friend and his girlfriend had decided to go on a short trip for the weekend, leaving me there alone. I wasn't too concerned, just figured I'd stay up all night playing video games, keep the curtains shut, and things would be fine. Well, at about one thirty the first morning, I was sitting on the sofa playing games, and the cat came over and sat in a chair a couple of feet away from me. At first he just sat there, but then he started acting strange, watching something in the direction of the kitchen.
I told myself not to worry and that the cat was just being a cat, but then the cat started to hiss and bat at the air in front of her, shying back as if someone was trying to touch her and she didn't want to be touched. I was absolutely terrified. Something was right there. I couldn't see it, but the cat could see it, and it was playing with the cat, and toying with me, too, if I had to be honest. I might have been able to write this off as well if it had just been a single bat and a single hiss, but this went on for an hour. A solid hour of the cat hissing, arching her back, hair completely on end. I couldn't move. I was too terrified to get up because I wasn't sure where this thing was, or what it would do. I ended up sitting there, unable to do anything but watch until it was finally over and the cat settled down again and I knew it was gone.
I immediately called my friend and told him that there was no chance in hell I was staying in that house for another night alone. He had someone else come and stay with me the next night, and after that I was getting out as soon as I could.
What amazed me more than anything, though, is that as soon as I left, I was aware of this massive shift in the atmosphere. That house felt so...oppressive. Negative, dangerous. It wasn't just that it felt malicious, it was depressing. It wasn't until I was gone that I was able to realize that it had been so strong. The same day I left, sleeping that night in a new place, I was just astounded at how light I felt.
It might not be as scary as other people's stories, but that place was absolutely horrifying, and I can honestly say that I hope I never have to experience anything like it again.