I work in a college of further education in Wiltshire, UK. The college is a brand new building which opened in January 2004. At the end of each term our premises/security guards would walk around the building to make sure all the lights are turned off in the classrooms and that the doors are closed and locked.
One day before the Christmas break, no one from premises or security were around so I said that I would wonder around the building and do these checks - as I didn't have any work to do and I knew that the building would be quiet as all teaching staff and students had left.

The college building is on 3 floors so I decided to start on the top floor.
As I walked around the floor, I had to close most of the doors and lock them. When I finished I had to walk back past some of the rooms to get the stairs to go down. But one of the doors was unlocked, wide open and lights on. This concerned me a little but I turned off the lights, closed and locked the door then carried on to the stairs.

I continued on to the next floor and then went down to the ground floor. After I had finished, I walked back up to the top floor to find the same door wide open, the lights on and the blinds open. This did start to freak me out. I went back down to reception, where I worked, and asked another member of staff to come up with me. When we got up there, we found 3 other doors had been unlocked and the doors wide open. Rightly or wrongly, we decided to leave the doors open. A few hours later our premises guys returned and I explained to them what happened. They said that this often happens and they usually leave the doors open - someone or something doesn't want the doors to be closed.

After doing some research we found out that the piece of land used to be a hospital for mentally ill people in the early 1800's, and that the patients would be locked in their rooms for hours on end. I don't know whether this explains why the doors won't remain closed or locked, but its certainly been a good talking point around the college.