I was a barmaid in a 15th century pub which was well known to be haunted.
One night just after I started I was locking up with my now DH downstairs and nobody else in the pub, I was wiping tables upstairs when I saw something in the mirror, looked up into the mirror properly and there was a man, turned round thinking maybe someone had been in the loo when i locked up but there was no one behind me and I decided it was my imagination, carried on wiping tables and there he was in the mirror again, called DH up and he said was it the man with shoulder length black hair and a white silk shirt on? then he explained every barmaid saw him when cleaning tables and that as long as he was in that room I was ok, sure enough a few weeks later I saw him stood in the doorway to the bar, about a minute later a man punched someone and there was a massive fight, years later another fight kicked off, this time in the garden, looked up and there was the man stood on the fire escape, a couple years after that he was standing at the window as I locked up, 2 hours later I walked past having nipped to a club for an after work drink and found the windows smashed.
On a much lighter note, I was locking up one halloween completely by myself, I'd been working there about 8 years by this point so locking up on my own wasn't a new thing or anything i was particularly bothered by, it was mid week and the town was quiet and the cleaner was off so i had stayed late to clean, I was just finishing cleaning the toilets when i heard a shaking of chains and thumping, all the doors were locked so I ignored it and washed the up stairs floors, went down stairs and the front door was shaking, looked on the camera and could't see anyone there so mopped the downstairs floor and went out to clean the back garden and have a sneaky cigarette and again i heard the door rattling and the chain shaking, went to look on the camera and still couldn't see anyone there, as I'm looking at the camera I hear the other door rattling, flick over to that camera and there is a ghostly pale face, by this point I've finished cleaning apart from the garden and decided as I'm opening in the morning I'll just lock up and come in early to clean in the daylight, so i lock up, check the camera and there's nothing there, so I set the alarm and leave, as I'm locking the back door i hear the chain shaking and door rattling again so I speed up my locking up and decide to walk the other way home, as I turn my back to the pub something grabs my arm, I scream and then i hear laughing, it was a barman from a local club, he'd been dressed as death for a party, had seen the lights on as he walked his girlfriend home so shook the door to see if i was in, which had rattled the chain we use to hold it open, then he had seen the lights still on when he walked back and decided he'd try all the doors to check i was ok as he knew I would usually have left by then and thought it was absolutely hysterical when he realised in trying to check up on me he'd creeped me out more than the haunted pub ever had.