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."