This unassuming flat stone, measuring roughly 0.9 metres in length and 15 centimetres wide, sits atop smaller supporting stones to form a simple altar. Known locally as the Mass Rock of Cró Na Roda, it represents a poignant chapter in Irish Catholic history when the practice of the faith was driven underground during the Penal Laws.

The site occupies a strategic position on rising ground beside what is now a mountain road, with sweeping views across the river valley to the southwest whilst sheltered by higher ground to the northeast. This southeast-facing location would have been carefully chosen; it provided both a vantage point to watch for approaching authorities and natural acoustics for the priest's voice to carry to the gathered congregation. The incorporation of the mass rock into the field boundary has helped preserve it, though its original setting beside the old road suggests this was once a more frequented route through the uplands.

These clandestine worship sites, scattered throughout Ireland's remote landscapes, served Catholic communities from the late 17th through the 18th centuries when attending Mass was illegal and priests risked execution or transportation. Local knowledge, passed down through generations like that shared by S. O'Beirne, keeps the memory of these hidden altars alive. Today, the Cró Na Roda mass rock stands as a tangible reminder of religious perseverance, its weathered surface bearing silent witness to the secret gatherings that once took place in this secluded valley.