I think the building I work in is haunted. When I've been the only one there in the mornings, I've heard footsteps, doors opening and closing, and the sound of water running in the bathroom sink. When I went to check out the water, no matter which way I turned the knob, I couldn't make the water stop. Another coworker, Erika, has said she's had a similar experience.
Erika works on the second floor, in what used to be a residence area before the building was converted into offices for us. The building was originally used as a carriage house, and is nearly 200 years old. She's said that she's heard the sound of people running around, and one time when she was in the bathroom, she saw the doorknob jiggling, as if someone was trying to get in. When Erika yelled out that she would be done in just a second, and for whoever it was on the other side of the door to stop, the only other person in the office called back that she wasn't doing anything, and that she had been in her office the entire time. The doorknob then stopped moving.
Another time, Erika was sitting at her desk by the open door. When she looked up into the doorway, she saw a shadowy figure, and thought that it was Klare, a woman who shared her office. Erika was about to ask Klare what she was doing, when she realized all of a sudden that the figure wasn't Klare at all, and when she looked back, it was gone.
We decided that because the offices that Erika works in used to be residences, chances are that there would be more paranormal activity there then elsewhere in the building, but still, I hate being there by myself, whether it's early in the mornings or late at night. Most of these occurrences have happened in the mornings though.