This story happened about 5 or 7 years ago.
Almost every weekend, I used to go with my cousin into the wilderness to chat and to drink beer. We would go to the same place as always; a derelict building, surrounded by meadows. We didn't have a lot of money, so we didn't hang around in pubs to save some pennies. As a rule, we would drink 3 beers there and then return home. However, it so happened we partied a bit longer and sat until dusk sipping beer. The building was devastated, rubbish and glass everywhere, a complete ruin.
That day, we were sitting at the very end of the building in one of the rooms. Someone had made a nice seat from stones. From there, we could perfectly hear what was happening in the entire building. If someone entered, we would hear it as the whole way was covered with broken glasses and bottles.
After a few minutes, a complete silence fell and we felt as if we were being watched. At one point, somewhere in the middle of the corridor, we heard someone stepping on the glass, walking slowly towards us. It surprised us, because the noises only began from the middle of the corridor and not from the moment someone entered the building.
After this someone had taken a few steps, they started banging on the wall and making inhuman noises. It was getting closer. We got up and wanted to jump out the window but my cousin said he would go check to see who was making fun of us. He left the room into the corridor and looked around the corner.
Suddenly, he took a step back and shouted, "Run!". Without hesitation, I leapt through the window, my cousin having such power and speed that it was hard to catch up with him. He was not especially timid, so what he saw must have been very scary.
I asked him later what he saw there, but he never told me. He told me that I wouldn't believe him anyway and changed the subject quickly. From that moment on, he became a little serious and turned from a prankster to a stiff. Not long after this incident, he committed suicide.
I don't know if it was related to this incident but I suspect it was. I knew him well. He was mentally strong and never complained about any problems. Even now, I wonder what he saw there and I have no idea and no chance to find out as the building was recently demolished. You might think it was just a bunch of drunken madmen messing with each other, but I know myself and I know we weren't drunk and I remember what I heard.
Some time later, I told my grandfather about this incident. The expression on his face indicated as if he knew who was with us at the time but he wouldn't tell me because, as he said, he didn't want to scare me any more and strictly forbade me from going there.
I think about it to this day.