Uminashizawa Sankyozuka is one of the mounds where 120 Christians working in the Tsunagi mines were executed and buried in three locations during the Kyoho era, and it is the only mound that has retained its original shape.
Stones engraved with scriptures and anonymous river stones are scattered on the mound. In the past, local people held the "Christian Village Festival" every June, and a pious mass was held here. (Currently not done)