I don't believe in ghosts, but I believe in a energy that's left after someone, as I've experienced it myself.
I've seen my passed away grandpa at a place he used to be almost every day, which was his boathouse.
I've slept in his room and felt his presence, I was not afraid, but felt relaxed...Because I loved him so much and missed him.
There has also been other case which were not so relaxing, when I was at my grandma's house, there was no one at home, NO ONE...And I were sleeping at the first floor. I tried to sleep but were constantly thinking there was something there, and suddenly someone/something bashes the wall on the other room...Never been so scared in my life.