According to the Times Online and writer Albert Jack, there are ten compelling mysteries that continue to haunt the world--in many cases for years and years after their initial appearances.
The Loch Ness Monster, (listed at number four), is a perennial favorite, not only for of the lovely, lonely setting of this legend, but because of the potential surprises that one might still find at the bottom of a deep, dark Loch.
But perhaps every mystery fan's favorite is Albert Jack's number two: the Disappearance of Agatha Christie in 1926--a mystery never really explained to the satisfaction of the public.
The most fun parts of this post, though, are the comments underneath it. :)