I've now written seven books that involve hauntings. And my six previous books are all about human ghosts - at least 200 of that variety. Actually, more like 400.
Some places have several ghosts.
But I must admit I've never seen a ghost myself. This is a bit embarrassing. I've occasionally been interviewed by talk show people who seem perturbed that I would write about ghosts without actually seeing one. Well, that shows how visually oriented some people can be. You don't have to see ghosts to know there are spirits hovering around, whether or not you can see them.