I used to work for my dad, who was partially self-employed doing regular maintenance and flour refinishing for a child care program called head start. The one center was in an old school, which was built not to long after the turn of the century, and served as a church functions building in addition to housing head start and another child care.
We always did floors over the summer. Anyone who has stripped and waxed floors knows that when you're putting the coating back on, it's quiet and relaxing. We were the only people in the building since it was a midsummer weekend, and yet it felt off, even before you enters, like someone was watching from the second floor windows. So here we are, making slow progress across this huge room, when we hear a think upstairs and stop. Then it sounded like someone was skipping across the room and back, a few times, and stopped again.
So we finished the layer and went upstairs. Mid you, the upstairs was a few claims with shelves (blocking direct movement from one end to the other) filed with supplies from the classes. Nobody was up there, so we closed the doors and went downstairs to start the other room. Once again, this sound started, but this time I sprinted upstairs. The sound speed before I reached the hall, but all of the doors were open at various angles.
We didn't hear the sound any more that summer, but my dad asked the child care adviser from the other end of the building if they heard weird noises. She said no, but that one day they were sitting down for snacks and a couple kids were staring in the corner. The aide asked them what they were looking at and one of the kids asks "why can't that girl eat with us?". The aide looked sound, then asked "what girl?" And the kid points at the corner and says "the little girl in the white dress"
I literally haven't set foot in that building since, and I have no desire to do so. I used to think ghosts were for scary stories but I have trouble believing this isn't real.
Sorry for any mistakes, I'm on mobile. Edit: Tried to change all "floss" back to "floors" because my keyboard is an idiot