In five days it will be the 733rd anniversary of the most famous missing children case in Western Europe. What happened to the children of Hamelin, a town (current population about 57,000) in what is today the German state of Lower Saxony (Niedersachsen)?
A June 2010 article in the Fortean Times by Maria Cuervo summarized various possible explanations; Cuervo reprints it in a more readable format on her blog here.
Years ago I read a science-fiction story of explorers coming to another planet and finding a human community who built their houses in a vaguely medieval German style. Yes, they were the descendants of the children led away by the ratcatcher, through some kind of interdimensional portal. If you know the author and title, post them in the comments.