Rob. WV, USA
Okay...minor case of the creepies. I am Head Custodian in an elementary school, an older building, built in the early 1960s. I had building check this past weekend, in June, 2018. You go in, look a few things over, check the temperatures on the coolers and freezer in the kitchen, and leave.
Now, in the summer the school gets really hot and there's no AC except in certain areas, so we have these big, industrial ventilation fans set up around the building, just to keep air moving. In the morning before work, I make a circuit and turn them all on; in the afternoon, just before we leave, I go around and turn them all off. When I went in to do my check on Saturday, the fan by the cafeteria was on.
I distinctly remember shutting it off Friday afternoon, as it was the last one, and the switch had given me a little trouble. There hadn't been anyone in the building since 3:00 Friday afternoon, and even if there had, why would they turn that fan on? Odd things do happen, sometimes; things disappear and reappear somewhere else or a hallway of classroom doors left open the night before will be closed in the morning, or vice-versa...the AC unit in the Main Office might be on, when you come in on a morning in winter. Other weird things.
One night a couple years ago when I was still working afternoons, the other custodian had just left the building, and I was getting ready to leave. I couldn't remember if I'd locked the front doors or not, though, so I headed upstairs to make sure. They were locked.
As I came back out into the darkened Main Hall and turned for the steps, I heard a voice say, plain as day, "Hi, Rob!"
I know I heard it. I stopped and looked around, thinking someone had come back in, and of course saw no one. I was the only one in the building... the whole big, dark building.
A teacher tells of how she'd stayed late one night (she said this was about 10 or 10:30pm, so both afternoon custodians were long gone), to prepare stuff for a substitute she had the next day. As she was sitting there in the quiet, she heard a door slam somewhere, off in the building. She gathered up her stuff and quickly left.
Another teacher was doing the same thing, late in the evening and alone in the building, and heard the side door, right down from her classroom, open and close. That door is always left locked during the school year and can only be opened from the inside, unless a key is used. She called out, and naturally, no one answered.
Supposedly, legend has it, a custodian had a heart attack and died in the building, in the late 70s or early 80s, so...