This is a thing I only learned recently, and damn, this sure is something. Love a good old unsolved mystery. The following is just a quick summary, you can easily fall into rabbit hole about it if you choose to.
So, pretty much everyone knows the story of the Pied Piper of Hamelin. It's a fairy tale about a ratcatcher luring away rats with his pipe to drown in a river, and eventually, after not getting payed by the mayor, children too. Or is it?
The most commonly known variant of the story was from a story collection by the brothers Grimm. But it actually wasn't part of their fairy tale collection, it was part of a collection of sagas and folklore. Also, all of their fairy tales end with a moral. This one just ends with kids disappearing and maybe drowning. Very much not a Grimms' fairy tale ending.
No, what this story really is seems to be a historic event turned into myth.
The earliest known mention of it was a church window from ca. 1300, which has been restored in modern times.
Curch windows have not only used to chronicle myths and legends, but also important historical events for the town they're in. This is also mirrored by the official town records, which mention a tragic event happening.
Also, notice how, in this wondow, we got the piper and the children here, but nowhere a rat a sight. Such an important part of the story would have to be somewhere, right?
Well, the earliest known mention of rats in this story is from 1559. Quite a leap in time. Since then, a lot of the story has been told by inscriptions into the walls of houses. Famous among them is the Rattenfängerhaus, "rat catcher house".
So anyway, something happened to this town. Lots of children disappeared at once. But what exactly?
That much is a mystery. Theories include the children being lured away by pagan cults. Or they were sold off into the Transsylvanian army, which was fighting off Mongolian invasions at the time.
But it could also be that the piper wasn't a literal person. Many the children died. Either by disease, natural disaster, or even a mass psychogenic illness like the dancing manias that were surprisingly common at the time. Because in that historic time period, many depictions of Death showed him as a piper.
But nothing concrete can be gleaned from anything we got. It's a mystery that will probably continue to remain one. It's all very odd. I for one have gained a new appreciation of the story.