Red Shell Town Natural History

This is a memory from childhood, when I was staying at my grandparents' house in Yamagata Prefecture and playing in a corner of what seemed to be a small town nearby.
Yet as he grew older, whenever he brought up that memory, his parents had no recollection of the town he described, and the protagonist himself could no longer remember where that town was located.
One day, while sorting through materials in his university research room, the protagonist happened to find a curious notebook. It seemed to record the history and various matters of a certain small town in the Tohoku region, but its contents were so wildly fantastical that it had been left forgotten deep in the document shelves. By coincidence, however, the protagonist knew the author of this notebook.
That person was none other than his uncle, whose whereabouts were unknown.
His uncle was a local historian who seemed to collect materials on neighboring villages. And within the notebook were records concerning the very town where the protagonist had once stayed.
It appeared that his uncle's notebook was a travelogue-style account of the history and matters of that town, but it was filled entirely with unbelievable entries and illustrations. Moreover, here and there were blank columns containing only an item name followed by notes like "details unknown" or "currently investigating."
Then, as the protagonist read through the notebook, he realized he recognized some of the items that had only names and no details. Come to think of it, perhaps this notebook was not entirely fantasy—perhaps some parts of it were based in reality?
Beyond the nostalgia for that town in his hazy memories, the protagonist developed a strong interest in the things written in the notebook. Fortunately, the school's long summer vacation was about to begin, so there was plenty of time. Though he probably could not help his uncle complete the unknown portions of the notebook, with the hope that he might discover something, the protagonist returned to his hometown.
And so, guided by the notebook, the protagonist kept recalling more and more, and at last arrived at the town from his memories. Just as his uncle's notebook had described, the town was a wondrous place full of strange things and customs.
In that town—"Benigarakucho"—the protagonist encountered all manner of "curiosities," and gradually came into contact with the mysteries hidden within the town, as well as his own lost past.