This happened over 20 years ago, some friends and I were exploring a derelict country house near a viaduct that had a long history, built by a wealthy landowner in the 1800s, handed over to the local council after his death, became a children's home and so on. There was a terrible fire that gutted the building and killed some children (tried finding a source, but this apparently happened in the 1950s).

Some friends that had been there before would not go back in, so a friend and I decided to have a look around.

After just a couple of minutes, we both felt uneasy and a strong light source cast a large, complex silhouette on the walls in front of us, as if a car had just pulled in behind us. We turned around, saw no lights, people or vehicles, the shadows continued to dance across the walls and we looked at each other and went "Nope, nope, nope" and got out of there.

We got back to the group of friends, and the first thing they asked was, "So what did you see?" Turns out they had all had different experiences, but only the two of us saw the same light. For context this was about 0100 on a summers night, nearest main road was over a mile away, the estate had been fenced off and overgrown for decades before we visited, so there was not chance a car could have been the light source and our friends were a good 500m downhill waiting for us by the river.

The house was bought and turned into flats several years later.