Kindaichi Shounen no Jikenbo, Karakurizoushi Ayatsuri Sakon Recommendations
Not sure who copied who, but the settings for the mysteries in the first few story arcs of Kindaichi Shounen and the story arcs of Ayatsuri Sakon are exactly the same. The castle and being stranded in an isolated mountain - all too familiar. But both are good regardless. And the mysteries are different even though the settings are strikingly familiar.
Both of these are mystery anime from roughly the same time frame that are forgotten, yet also not forgotten.
Compared to Ayatsuri Sakon, Kindaichi is your stereotypical shonen hero: He takes action, loud, funny, good hearted but deep down he has a sharp wit. At first, this might seem like a huge contrast to Sakon, considering how shy and soft spoken he is but the overall plots of these two series are pretty similar. At first the cases present themselves as supernatural, but soon the protagonist unravels the truth. If you enjoy mystery animes and are looking for something similar to Sakon but a little more lighthearted, Kindaichi is a great follow up series.