Most ringforts, the circular or near-circular enclosed settlements that were built across Ireland roughly between the early medieval period and the Viking Age, are conceived in the popular imagination as tidy rings. This one, sitting on a west-facing slope of a ridge amid grassland in Carrowculleen, is distinctly D-shaped, measuring around 33 metres on its north-northeast to south-southwest axis and just under 29 metres across. The asymmetry is not decay; it is the original form.

The site was recorded under its local name, Gannon's Fort, as early as 1914, a detail that suggests the name had already settled into the landscape long before anyone thought to write it down. A rath, as ringforts defined by earthen banks are sometimes called, typically functioned as a farmstead enclosure, protecting livestock and a household rather than serving any strictly military purpose. At Carrowculleen, the enclosure is defined by a bank along the north-northeast arc and by a scarp, a slope cut into the ground, elsewhere. Crucially, a fosse, meaning a defensive ditch, and an outer bank survive along the stretch from west to north, giving the western side of the fort a layered, more elaborately defended character. Whether that reflects the lie of the land or a deliberate choice of construction is not clear, but it gives that side a different quality to the rest. Two further monuments sit close by, another ringfort and an enclosure, roughly 130 metres to the southwest and west respectively, which raises quiet questions about how this small cluster of sites might have related to one another.