I was working an overnight shift in an old textile mill. The mill was 117 years old. I had to stay overnight to keep an eye on a leaky water main where it entered the building. By 11pm the building was empty. I made a quick tour of the building just to satisfy myself that I was alone. Security had gone through before me and when they left they told me I was alone in the building as well. It was about 11:30pm when I returned to my post to watch the pipe leak slowly. There wasn't much to do in the small space so I started to read a book.
It was about 12:30am when I heard a muffled conversation outside the space I was in. I got up and stuck my head out of the room and looked down the hallway but there was no one there. I sat back down and picked up my book and I heard it again. This time I walked out of the office and up and down the hall. I checked each room and found no one else there. Now this is a 3 story building and I only checked the first floor, the floor I was on. I sat back down and read for a little while longer. I needed to stretch so I took a walk.
I went to the third floor and walked the main corridor. Everything was quiet. Same thing on the second floor. I looked out the windows and saw my vehicle was the only one in the lot.
It was about and hour later and I had made my tour of the building and heated up a dinner. I was sitting in the space with the leaky pipe eating dinner when I heard the muffled voices again. I ignored it this time and eventually they either faded away or I tuned them out. I sat there and read for about an hour after I ate with no other noises.
At 3am I got up to go to the bathroom. I walked down the corridor passing 4 offices before getting to the bathroom. All was quiet and dark inside the offices. I did my business and washed my hands and walked out of the bathroom. I noticed the office nearest me now had a small desk lamp on. I didn't see anyone in the office so I stuck my head outside to see if a car was here. There were none. I went back inside and looked around. I called out a couple of times but got no answer. I mustered up some courage and entered the locked office where the desk lamp was shining. I looked around and there didn't seem to be anything out of place. I shut off the light and backed out of the room. I pulled the door tight and backed away.
Just as I left the corridor and entered the space with the leaky pipe I heard a door slam. I may have made a noise myself, may have let out a startled scream but I am not sure. I looked back out, down the corridor and I saw nothing. I was pretty well freaked out but I managed to walk down the hallway. When I got to the last office near the bathrooms I noticed that the desk lamp was back on. I didn't bother turning it off again. I went back to my space and sat listening. I couldn't even concentrate enough to read. I just sat and listened. The voices would come and go. Sometimes nearly loud enough to make out the conversation but never quite. As the sun rose and the light made it's way inside the building the voices ended.
The first shift worker arrived just before 6am and I couldn't wait to get out of there. It was just too creepy for me.