What makes it unusual is not just its age but its layering of purpose: a pre-Christian or early medieval bullaun stone, a large boulder with a natural or hand-deepened hollow that has long been associated with ritual use, sits to the north-north-west of the structure, its hollow filled with coins left by recent visitors. A stone cross stands upright at the centre of the altar itself. Two trees have since rooted and grown out of the masonry, and the monument now has the look of something the landscape has been slowly reclaiming, though it is clearly still tended.

The altar is a wedge-shaped drystone structure, meaning it was built without mortar, using carefully fitted stones, and measures roughly twelve and a half metres in length and just over three metres wide. It faces north-north-west. According to a 1908 account by Glynn, Mass was offered here during the early Penal Laws period, when Catholic worship was suppressed under seventeenth and eighteenth century legislation and priests were forced to celebrate the sacraments outdoors at improvised sites known as Mass rocks. This particular structure is more substantial than many such sites, and the presence of the bullaun stone suggests the location may have carried religious significance well before the Penal era. Bullaun stones are found across Ireland, often near early Christian sites, and are thought by some scholars to have pre-Christian origins, though their exact purpose remains debated.

The site sits in grassland on the north bank of the Beagh River, and the coins in the bullaun hollow suggest it continues to draw people with some devotional intent. Whatever drew worshippers here in the penal period, the place does not appear to have been entirely forgotten.