It looks, at first glance, like a quirk of the landscape, something a glacier might have deposited and forgotten. In fact it is a boulder-burial, a prehistoric monument type in which a substantial capstone is raised on smaller uprights to form a low, table-like structure, generally understood to mark a place of interment or ritual significance, though their exact function remains a matter of ongoing study among archaeologists.

The boulder measures roughly 2.7 metres by 1.85 metres, with a thickness of around 0.8 metres, making it a considerable presence in the otherwise unremarkable field. It was recorded by Ó Nualláin in 1978, and noted again in the Archaeological Inventory of County Cork published in 1992. There may be additional support stones beneath the surface that are no longer visible, and a second large boulder has been incorporated into a roadside fence about 13 metres to the south, though without visible support stones it cannot be confidently identified as a second example. What makes the Ballynacarriga site particularly interesting is that it does not stand alone. A further boulder-burial lies around 100 metres to the south-south-west, and another is recorded approximately 250 metres to the north-east, suggesting this stretch of ground in the hinterland of Garnish Bay was once a meaningful part of a wider prehistoric landscape, one in which the placement of the dead, or the marking of territory, followed patterns that are now only faintly legible.