My father works as a maintenance manager at a large old church in the southwest suburbs of Chicago, and as a kid, I'd often go with him on Saturday mornings and have the whole building basically to myself to explore. (It was composed of the church itself and a modern addition of offices and a nursery school).
The one morning, my dad told me that they were cleaning up the basement area under the church itself and there were boxes of old magazines that I could look through, and to take any I liked before they were thrown out.
He brought me to a dark area right under the main entry hall of the church, which was built as a "lounge". One side had ladies' restrooms, the other, mens'. In between was an open room with benches with horsehair filled cushions, dark wood, and narrow stained glass windows.
The boxes were in what was the ante-room of the gentlemen's restroom, now stuffed with things ready to be tossed out, much of it dusty. The place just smelled musty and unused, but I was interested to see the old magazines from the 60s and 70s.
My Dad found a folding chair and told me he'd be back when we were going home, in a couple hours.
The small dingy room was lit by one light bulb, and another narrow stained glass window (which looked like it hadn't been cleaned since the place was built). I was pouring through the old Life, Look and Time magazines for maybe half an hour, sitting there with my back to the open doorway leading out to the open area, when I all of a sudden felt someone watching me from behind in the doorway.
I assumed my dad had come back down to tell me something, but when I turned around, no one was there, despite the distinct feeling someone was standing right there a second ago.
I got up, walked out and called for my dad, but of course no one responded. I walked up the stairs and looked around for him, but couldn't find him anywhere in the church so I went back down, shaking the feeling off to my imagination and returned to the room where the magazines were, but now the room felt chilly, but only right when you walked through the door frame, but if you took a step in either direction, it was stuffy and warm. There was no vent anywhere, so I couldn't figure out where the coolness in that one area was coming from, but again, I shrugged it off and sat back down. As soon as I picked up another magazine, I felt the eyes boring into the back of my head again, and it was not a pleasant feeling. I slowly got up, set the magazine down, turned around, and, my heart starting to pound quickly. Walking very quickly (but not running) I passed the cool area, where the feeling of being watched was emanating from, and then ran up the stairs, out of the church itself, and into the nursery school area, where I found my dad.
I asked him if he'd come down there again since he'd left, and of course he said he hadn't. He asked if I'd found anything interesting, and I said no, not really, though in fact I had in a way, or more correctly, something had found me, and I wasn't anxious to go back down and share that room with it again anytime soon.
A few years after that, after the area had been remodeled for Sunday school classrooms, I'd gone back down there, with my dad, I still couldn't bring myself to go down there alone, though I was in my late teens by then, it was bright, well lit, and there was nothing eerie about it whatsoever.
I hoped whatever it was watching me that morning was happy with the new look if it was even there anymore.