The informant shares the legend of Rannariedl Castle in Upper Austria:
My informant, a native Austrian couch surfing across North America, said that he knew this story because he learned it in school, but that he remembered particularly because the castle, or at least the remains of the castle are 20 km (~12.5 miles) away from the house that he grew up in.
The legend is one of stolen property, which, after many hardships, is serendipitously returned to the rightful owner who had always been a good man. Many different folklore tropes come into play here: the idea of good karma and what goes around comes around plays a large role in the story, as does the idea that eventually, everything will find its rightful place.
Seeing as the story was taught in his history class, there is a large base of belief surrounding the happenings of the story itself, even if it was hard for me to find similar, and as detailed evidence of the truth-value of the story, particularly when the infant boy is sent down the river in a walnut shell. However, it could be possible that there was something lost in translation in the informant’s performance of the piece, seeing as English is not his native tongue, even though he speaks it very well.
This legend can also be found here (text in German, legend is number ‘*104’): http://www.sagen.at/texte/sagen/oesterreich/oberoesterreich/allgemein/schatzheben.html