What's your favourite horror related folklore/myth story, how scary was it, and where does it come from?

There are countless horror oriented short stories…these days, you usually find them in children’s books, and when I was little I read a whole bunch of them. These kinds of tales often seem to survive from one generation to the other orally, or find themselves in books as I’ve mentioned, and plenty of them go through variations…
One of my favourite ones ever is Tailypo, which I’ve read countless different versions of, and in two different languages…ancient spooky tales take all sorts of shape; short stories, urban legends, fairy tales of some kind or another.
So they can be anything, as long as it’s generally known as a ’‘scary’’ story…so, which is your favourite?
As I say I read so many when I was younger but I think I forgot most of them, so perhaps the answers here will ring some bells, or introduce me to new stuff.