(All names in this account have been changed for privacy reasons)
My cousins have this huge property in a rural area, basically in the middle of nowhere. They have a huge farmhouse, a barn, stables, everything. Every year, for Thanksgiving, we (my family and I, along with other relatives) drive up to their place to celebrate. They have a huge house, and it has plenty of space for everyone.
It was weirdly really warm for November, like short-sleeves weather, so the parents expected us to play outside. The eldest cousin, who I'll call John, suggested we play hide and seek. Before we ran off, he pointed to the abandoned guest house and said that it was haunted. We snickered because John was a big liar and no one believed him. But, oh boy, he sure was right.
George, my aunt's son, who was my age, dared me to hide in the house. I looked at the dark, paint-peeled house. I didn't want to seem like a baby, so of course I went.
I creaked open the door and snuck in. I took a creaky, decayed set of stairs to the second floor and ran into the first room I saw. The floor was covered in some wet substance that smelled metallic (blood?) but, the only thing on my mind was hide and seek. I hid in a closet and sat down. There was a black cloak hanging in the closet, and I hid behind it. I was there for a good 15-20 minutes before I heard the door downstairs creak open.
A little boy giggled. I figured it was George, but then they started going upstairs. The footsteps stopped in front of my room. I froze, trying to stifle my laugh. But then the boy stepped in. He wasn't George. He was pale and covered in blood. He sat on the floor, giggling for what seemed like an hour. I couldn't look. Then it stopped. I ran out of the closet and floored it downstairs. I ran inside where my parents were about to call the police. I spilled everything. John gave me a look. "I told you not to!" He said.
Turns out the same thing happened to him when he was little.