This happened in a hilltop schoolhouse in a small village in the country. My best friend lived there with his parents on the top floor. The bottom floor was the school.
I knew this friend for about 10 years before this event. He told me numerous stories of paranormal events at his house, some of which were so fantastic they were very hard to believe indeed. Like both his parents seeing a stagecoach whizzing by on the village road at night at breakneck speed and a man firing a pistol at it. It all looked like it was in the 18th century. I thought the same thing as you probably are doing right now; yea, right. But unlike many other people I never caught this friend telling a lie or even exaggerating or embellishing. He also told of the whole family gathered in the kitchen hearing footsteps in the hallway getting closer to the door.
It was the same sound like they heard before when people came to visit them. But when they opened the door to see who was there they found an empty hallway. This is the kind of story you read about on this site a lot and it seems to occur fairly commonly.
I stayed at their top floor apartment for several weeks on different occasions and neither I nor any of the family noticed anything. Then one time we were sitting in the teachers' room (his mom was the principal and had keys to the whole place) discussing things we wanted no one to hear. It was around 3:30 am. My friend said, "That's weird. The keys are bobbing around in the lock." (He had locked the door from the inside and left the key in the lock along with the other keys which were on a ring.) I looked and sure enough they were dangling. No one but us were in the room.
I felt a sudden burst of excitement that I was going to witness something supernatural and jumped off my chair to inspect the door. My friend followed. We checked the hallway. No one was there. The school was being renovated and in the hallway there were doors that had been taken off their hinges leaning against the wall on their sides. From behind one of them we were standing close to, we heard three knocks, although neither of us was close enough to have done it. I immediately inspected what was behind the door and there was nothing.
Then I started strutting down the hallway and said quite loudly it was probably the people who got tortured and killed by the Germans during the war and that they just wanted respect. (The schoolhouse was used by the Gestapo during WW 2.)
Then nothing else happened and we went back to our conversation.