Not my story but one of my favorites:
I was renting a basement apartment a few years back. The place sort of sucked. It was cold as hell and obviously not intended as a bedroom, with exposed cinderblock for 2 of the walls, but hey as a student you take what you can get. At night I kept hearing this scraping noise from the walls right under my bed, sometimes slow and deliberate and at other times a sort of skittering, frenzied sound. I had assumed that there was some sort of animal nesting in the wall and mentioned in to the owner. He said the foundation was improperly laid and moles and rabbits could occasionally get in between a couple of blocks. He said they couldn't fix it before I'd moved out (I bet he said that to all the tenets) so I just put up with it.
One morning I woke up and there was dust all over the floor of my room, and a big smear of it on the pillow next to my face, with my window wide open. The best rationalization I had at the time was I had left the window open and maybe some dirt from the construction down the road had blown in while I was sleeping. I put it out of my mind and life went on. From that night forward, though, I didn't hear any more scraping from the walls.
Later, when I was moving out, when moving the bed out of the room, I noticed it. Underneath the bed there were little cinderblock chips and an old rusty railspike, along with a hole in the wall about a foot an a half wide. I still remember the feeling spotting that. My blood turned to ice and my stomach knotted up. The hole was impossibly dark, none of the light from the room even seemed to touch it. I ran upstairs and grabbed a flashlight from one of my boxes and shone it into the hole. There was a little crawlspace, completely bricked in. No way in or out save the newly-opened hole into my room. The walls were covered with geometric patterns scraped into the brick. Squiggles, triangles, what looked like a distorted stickman. Layers and layers of them, some faded and hardly visible, other freshly carved. The floor was covered in a thick coat of dust and little shards of rock. In the corner there was a straw doll stained red.
I had been sleeping in a bed inches from this for one and a half months. Two and a half months mere feet from whatever the fuck had been in there previously. I don't much like dust anymore.
(Link to original post:) [http://www.reddit.com/r/AskReddit/comments/pwwoq/tell_me_your_scary_stories_reality_or_fiction/c3szpcg]