First let me begin by saying if you don't believe in the supernatural that's fine.  But I do because I have seen and heard things for years that others around me haven't.  
I currently work at a drug manufacturing company outside of pittsburgh.  They have a modest 4 story corporate headquarters here.  All 4 floor are broken into 2 section.  Each section houses a different department.  The first floor is seperated into legal and the main lunch room/meeting room.  2nd floor is finances and taxes.  3rd floor is it and hr.  And finally 4th floor is 2 executive wings.  
Now to access these individual wings one needs a key card to open doors.  At night on camera doors will open by themselves.  I have seen it happen multiple times in person and through the camera.  The worst section for this is the second floor which has a landing that over looks the first floor lobby.  On this landing things move around all the time while the security guard is right below sitting in the lobby.  We can watch things move on the camera and hear it.  I have personally seen a chair move from one end of the landing to the other.  When this happens we have to time stamp the video for corporate security management.  (They like to edit those things out of the videos.)  After these things happen we have to move all items back to their previous locations.
The next area is a small hallway between finance and tax.  there is a mothers room back in this hall for pregnant mothers to milk themselves.  We have seen orbs back here.  One guy said he saw glowing blue eyes here.  I personally have only felt like I was being watched in this area.  But others have told me that they have heard whispers and footsteps here as well when no one is in the building.
3rd floor.  We have a dark hallway where everyone is overcome with an impending sense of dread.  One guy quit the job saying he saw a shadow person in the hallway.  I have personally not seen anything in this area, but i have heard footsteps following me.
4th floor is relatively calm.  Except the main executive wing.  Here there are voices that can be heard.  we have multiple guards that have said they've heard curse words whispered at them.  I am one of the guards that have experienced this.
Nothing really happens on the first floor.  Just some bangs and pops, other than that it's quiet.
I wish i could snag a video to show everyone, but the cameras are hooked up to a dvr system that is locked in a network room.  The only people with access are the security managers, and they don't want people to know how active the building really is.
Security personnel are not the only ones that go through this.  We recently had a cleaner quit and walk out because she saw a door open on the 3rd floor when no one was around.  She came right up to the front desk dropped off her gear and left without saying anything at the time.  She later told her supervisor what had happened.
If you guys give me a few weeks I will tell you what company and where the building is located.