A young American tourist goes on a guided tour of a creepy old castle.
At the end of the tour, the guide asks her how she enjoyed it. She admits to being a bit worried about seeing a ghost in some of the dark cobwebby rooms and passages.
"Don't worry," says the guide. "I've never seen a ghost all the time I've been here."
"How long is that"? asks the girl.
"About three hundred years."