This is a cashel, a roughly circular drystone enclosure of early medieval origin, but what sets it apart is the sheer mass of its construction: the wall measures 5.2 metres wide at its western stretch, and at least one additional face lies hidden within it, suggesting the kind of multi-vallate engineering more commonly associated with the great stone forts of the Atlantic seaboard.

That architectural link is significant. Researchers have grouped Caherbullog with what are termed the Western Stone Forts, a category that includes the famous clifftop forts of the Aran Islands as well as nearby Burren examples such as Ballykinvarga and Cahercommaun. The cashel measures roughly 34 metres north to south and nearly 33 metres east to west, giving it a substantial footprint even in its compromised state. Field clearance has been piled against its outer wall and heaped inside the interior, making detailed inspection impossible for now, and an entrance believed to survive beneath the rubble remains inaccessible. Later field walls radiate outward from the perimeter at the north-east and south-east, a sign of how thoroughly this landscape was reorganised in more recent centuries. The site appears on both the 1840 and 1916 editions of the Ordnance Survey six-inch map under the name Caherbullog, and it shares that townland with a second cashel. The antiquarian T. J. Westropp noted in 1901 that these two enclosures, which he referred to as the "two Caherbollucks", had an unusual documentary afterlife: both were surrendered to the Crown by Sir Tirlagh O'Brien, then regranted to him in 1583, a transaction that places these prehistoric-looking structures squarely in the upheavals of Elizabethan Ireland.

The site sits on a narrow shelf on the western side of the Caher valley, about 240 metres from the Caher River, in land that has been extensively farmed and reshaped over the generations. The accumulated field clearance that frustrates archaeologists also, in a way, tells its own story: the enclosure has been used as a convenient dump for generations of stone-clearing, which means that what looks like a modest ruin may be concealing considerably more than is visible from the outside.