I don't really believe in ghosts, but ever since I got a job valeting at a historic hotel that is getting renovated, I can't explain some shit.
Inside:
Basically one night, my manager had me and a security guard to help him search this 18 story beast (which happens to be totally vacant and pitch dark above the 2nd floor) for a possible hobo that they thought was living there. Both my manager and the security guard are big guys and they just brought me because I wanted to check out the rest of the building. I didn't even get a fucking flashlight only the other two did, and we had to check room by room. So basically, from floors 18 to 14 everything went cool. It was weird because there was offices and apartment rooms that still had tons of shit in them, even one room had a few manican heads in it which gave us a good scare, but nothing strange happened and we were just exploring so it was kinda cool.
Then we got to the 13th floor. Now I never knew that most buildings don't have an actual 13th floor and the security guard made sure to let me know to scare me, but I didn't think anything of it. So we started on the right wing of the floor in an old law office. We end up in this little law library and there are a shit ton of books all numbered because they are a series that you can buy or something. As, we are looking at the books we noticed that only one book is backwards in the shelves. Of coarse it was vol. 666. We were all like "what the fuck!" but we figured when the person left they were just playing a joke for later. So just as we started leaving the room we heard a door slam....We all heard it, we were all next to each other, we were all like fuck this. So we decided to skip the the other two wings and continue to the 12th floor which was even more fucked.
The 12th and 11th floor were the old hotel rooms from the early 1900's that haven't been turned into office space or apartments over the years. Every thing was super old and creepy and we were already all paranoid. We checked the right wing and were about to check the middle wing when me and my manger heard a bunch of noises coming from down the hall. We both acknowledged that we heard something moving around down the long dark hallway. The security guard who was like 10 feet back did't hear anything, and started to make fun of us. Then my manager told him to be quite and proceeded to calling out to nothing in the hallway "Hey buddy how bout you do that again for us." Right as he said that it immediately started moving around for a few seconds and then stopped.
That was it for us we had enough and went back to the ground floors. We were all freaked out but when we got down we had good laughs telling everyone what happened. I would defiantly go up there exploring again (There is a floor that was an old nursing home or something, and the basement has weird old pools and shit) but I will never do it at night that place is fucked, and I have no explanation for anything that happened.