I work as a security/nighttime attendant at an apartment building. It's 24 stories and one of the oldest buildings in the city.
One night I'm sitting here when the phone rings at about 3 AM, and I answer "Hello this is draven at the front desk how can I help you?" the voice on the other end sounded female, but was totally garbled and the only bit I could make out was "23rd floor." I tried to tell the person I couldn't understand them, and asked what apartment they were in, but again garbled response and "23rd floor." After the 3rd time of trying to understand them and the same response, I said since I couldn't understand them I'd come up and to meet me in the hallway.
So I go to the main elevators, and both are up on the (surprise) 23rd floor. Luckily, we have an older service elevator and it's only on the 7th floor so I call it down. I get it and hit the button for the 23rd floor, but it won't move and the inner door won't close, so I go to unlock the reset panel and boom we start going up, door still open. I'm freaking out, and the elevator is shaking because it goes pretty fast and is old. As I'm going up, I just stay towards the back and finally I reach floor 23.
I step out, door closes just fine, and I look around the hallway. There's nobody around. I walk along slowly trying to listen for anyone awake who might've called, but there's nothing. So now I head the opposite direction and go towards where the regular elevators are and when I get to them they are just sitting there with their doors open. I was pretty freaked out but I knew it could just be the elevators on the fritz, so I get in and figure I'll just reset them when I get to floor 1 when I hear the sound of the back stairwell closing. So I quickly get out and go to the stairwell and lo and behold, no one's there, but the maintenance door to the machine room is ajar, and at that time I'm the only one in the building with a key. At the top of the building is a large machine room housing all the really really loud machinery that does stuff in the building and allows access to the roof. I don't like going into it because it's creepy as fuck and no one ever goes there, so at this point I'm seriously freaked out but I muster up and head in.
I shout "Hello?!" and there's no response. The lights in this room flicker because they're shitty fluorescent so I can't see well either, but at the end of the room I can make out the roof access door and sure as shit, It's slightly open. So I slowly continue forward checking the space in between each machine as I walk by, and there's no one there so I open the roof access door. I can't see anyone ahead of me on the roof but there is a slight wrap around and if there was a jumper or something I needed to be sure so I step out and leave the door ajar like it was.
Almost immediately, the door is pulled shut. Now I might've written it off as wind or something, but this door is hard to shut and hard to open. Really hard. I immediately grab the handle and hank it open, slam it behind me and run straight for the maintenance door. It automatically locks when it's closed so I slam it shut too and go back to the 23rd floor hallway, get into an elevator (doors still open) and go all the way down to the first floor. I go back to the main lobby and as soon as I sit down, the phone rings. I pick it up, don't say a word, and sure as hell garbled voice again only audibly saying "23rd floor." I hung up the phone, turned the ringer off and spent the rest of the evening just staring at the parking garage security monitor.