In fact the place carries two names that tell its double nature plainly enough: Carrig an Aifrinn, meaning Mass Rock, and Poll an Aifrinn, meaning Mass Pit, the second name referring to the many bird's-nest-shaped depressions that surround the stone. Folklore collected from Castlemaine school noted that these hollows could conceal hundreds of people from view even at a distance of ten yards, which was precisely the point. Mass rocks were the improvised altars used by Catholic priests during the Penal Laws, when public Catholic worship was banned under English colonial legislation; congregations gathered in remote fields, bogland, and woodland rather than risk attending formal services.

The wood at Killaclohane offered unusually good cover, densely planted at the time with larch and oak, but it was not always enough. On 7th June 1651, two priests, Father Cornelius McCarthy and Father Thaddeus Moriarty, were captured at the site while conducting what was called a general station, a gathering at which confessions were heard and Mass celebrated for the wider community. Both were taken to Fair Hill, now known locally as Martyrs Hill, and executed there. The congregation and the other priests present escaped. The local tradition, as recorded by schoolchildren in Castlemaine, is careful to note that point, the survival of the many alongside the deaths of the two. The site also carries stranger stories. One account describes a group of young men who went out torching in the wood on Christmas Eve, a night-hunting practice using makeshift torches to dazzle birds, only to find their lights failing and themselves stranded in darkness at midnight. They heard a bell ringing from Poll an Aifrinn, louder and clearer than any church bell heard on a Sunday morning, and made their way home, never going out on Christmas night again. The tale was offered in the original account as a true story, one that had happened within living memory. In the vicinity of the rock, the same local tradition records mounds, curious stones thought to be early grave markers, and a few cromlechs, the term used at the time for megalithic structures such as portal tombs. The site was still being used for religious purposes well into the nineteenth century: according to the same collected folklore, a woman described as an Indian princess, who had come to stay at Kilcolman and converted to Catholicism, received her first communion at the Mass rock, the ceremony conducted by a Father Batt O'Connor, then parish priest of Milltown. Names, carved into the rock across generations, remain visible there.