I love a woo thread!
One experience really sticks out for me - I've told it before on here but it's that time of year again... 
Years ago I had a boyfriend who loved looking at old ruins. There was a stately home in the middle of nowhere a few miles from us which he had heard you could just wander straight into - over the years the fences around it had disappeared. So we went for a look with a small group of friends.
We had to park a fair walk away, and when we got there we had to edge down a steep overgrown hill to get to the house, which took a while. At the bottom, the whole of one side of the house had gone, and you could walk down straight into the basement, which had various corridors going off into the darkness; it was a bit creepy but fascinating. My noseyness overcame me and I went off alone down a corridor where the light was getting very dim. I turned a corner and suddenly right in front of me was a man, as solid and real as you or I, but he looked kind of grey and almost lit from within, if that makes sense. He was standing in a really strange way, really upright and straight up against a wall, facing it, and he was wearing a military uniform with a peaked cap. I must have gasped or screamed and as I stopped he turned his head really slowly to look at me, but didn't speak or move.
I turned and ran back out towards daylight, shouting that there was someone in there. Everybody else appeared from various places and started running with me and freaking out - the funny thing at the time was it must have taken us about 15 minutes to get there, but we were out of the place and up the hill in about 20 seconds 
Most of us ran back to the cars, but a couple of people hung around at a safe distance from the entrance to the basement to see if anybody came out - and nobody did.
I was really spooked but convinced myself (with the help of everybody else) that it was just somebody hanging about, maybe a security guard (although it made on sense that he hadn't spoken or followed us out...). I also could never shake the fact that he looked 'odd'.
Years later there was an item on the local news about the place, because it had been bought by a company who were going to restore it to use as a wedding venue & hotel. The reporter went on to say about how the hall was last used in WW2 as an RAF HQ and showed pictures of men in their peaked caps and uniforms in the buildings during the war.
The hairs on the back of my neck went up and I spent the rest of the night googling it. I am now completely positive that what I saw was a ghost
.