Ok, so another one
I used to work for an outdoor adventure centre in shropshire. One of the main accomodations was a large ancient mansion house, that been previously used as mental institution and then more recently, a borstal. It was generally a very creepy place, parts of it were very cold, other parts were melting hot. They only used it for accomodation in the warmer months, due to its size it was very hard to heat.
At the beginning of the season one year, in February, I was doing my evening entertainment in the mansion house, and there was no one staying in at all since it was winter. The entertainment was egg drop, where the children made parachutes for the eggs, and dropped them down the middle of the staircase from the top floor, to see if they survived.
So I was on my own with 25-30 children, they were all tailing behind me while I ran ahead up the stairs, switching the lights on as I went. I got to the middle landing, where there was a toilet with a frosted glass window. As I stood there on my own, a figure walked past the window, pausing for a second or so to look at me. I could only see the dark shape of a person, but felt them looking at me. Behind the door of the toilet, was a brick wall, and this is where the person seemed to walk straight into.
I freaked out a little bit inside, trying my hardest not to terrify all the 10 year olds I had with me, and just shouted at them all to come and help me turn the lights on and we'd all go to the top floor together. It was incredibly creepy, the mansion house always had such a heavy atmosphere and it was so cold and dark that night.
There are loads of other stories from that place, including my friend walking into the staff room, and his surroundings turning into what it would have been years ago when it was an instution. Another one was loads of people spotting a little boy with a bleeding nose, always alone, and wearing old fashioned clothes, and no one could ever place him to any particular group of children and was seen through the whole summer.
sorry, that was long!