I worked in a restaurant/bar that was part of a chain in Pittsburgh, Pennsylvania. The decor and menu were designed to have a medieval English feel. The owner bought many items to decorate the restaurants while on a trip to England, including many antiques. The story has it that a ghost came along with the antiques, having some connection to them.
The building had no windows so unless the lights were on the restaurant could have a very eerie feeling to it. On a Sunday in February of 1989, three of us were working in the kitchen getting ready for the day. It was shortly before 1 o'clock in the afternoon, and we were expecting others to start showing up as the restaurant opened at 2 o'clock on Sundays. For some reason I looked out of the kitchen through the pantry and I saw somebody standing there with black pants, a grey tweed coat, and a regular looking white hand (I could not see the face for it was blocked by a shelf in the dish washing area), and then they walked off into the bar. I said to my two co-workers "Someone's here." They looked puzzled as we had not heard anything or anybody, and I was reminded that if someone had entered the building by any entrance we would have heard it for the doors made a lot of noise when locked, unlocked, opened, or closed.
Since we kept the doors locked until we opened for business we decided to look around to see if someone had come into the building. We checked the doors and they were locked. We then looked in the bar, both dining rooms, the restrooms, storage room, lobby, and breakroom (the office was locked so we couldn't look in there). We found no one. All we could think of was the ghost had been watching us work and when spotted decided to get out of view.
This was the only experience I had but I had been told many others. The ghost didn't seem to be a harmful sort, just curious and a bit of a prankster.