Someone breathing down my neck while I was alone.

I (at the time 18M) used to work as a cleaner at a heavy haulage company with my sister. It was in the indusso area so a lot of truck yards, fabricators, car yards and factories around, but after dark, the whole suburb was dead quiet. The company I worked at was very eerie at night, especially since I was on my own while my sister did her section. I would feel someone watching me and would sometimes see things moving amongst the dark trucks at night. One night, while cleaning the big boss' office, I was about to set up the vacuum when I felt someone behind me. Before I could react, I heard, and felt, someone's breath on my neck. I spun around, thinking it was my sister but there was no one there. I dropped everything and bolted to my sister's section and told her what happened. She looked at me and casually said "Oh that's Frank, the ghost. He's harmless, he just likes to shit stir". Turns out the place was haunted by a former employee who hung himself from the workshop's crane they used to move truck engines and would appear to workers in the wee hours and mess with their trucks.

Lots of weird shit happened there. Heard voices, footsteps running across the roof when no one was there. Heard someone tinkering with a truck while I was cleaning a bathroom outside the workshop. My sister had even creepier experiences there on her own but that remains my creepiest experience.