As it's almost Halloween season (for what it's worth) and because I have gone through every previous thread of similar stories.
I have a few but the first one that comes to mind is that a distant elderly relative lived in a dormer bungalow. The whole house felt oppressive and dark. I can't explain the feeling. I was maybe 13. If I went to the loo I would make someone else come with me.
One day, for some reason, my dad showed me the upstairs of the house and it was even more awful feeling than the downstairs. It was literally a bedroom and a tiny en-suite. No one else in the room but there was an indentation in the mattress that looked like someone was sat on the end of the bed. Stared at it for a bit and as I went to point it out to my dad it slowly raised back up to normal size.
When I tried to broach it with elderly relative she was so blasé about it that it made me feel a bit stupid. She was like 'oh yeah, built on an Indian burial ground (in north Lancashire) so I get lots of visitors'
I've only ever felt that oppressive feeling once since in Edinburgh castle (not in the dungeons)