Those ridges are the traces of cultivation, evidence that at some point the enclosed space was worked as farmland rather than simply defended or inhabited. It is a small detail, but it complicates the usual picture of a ringfort as purely a settlement enclosure, and it has left its mark on the grass.

Ringforts, sometimes called raths, are roughly circular earthwork enclosures, typically dating from the early medieval period in Ireland, and were most commonly used as defended farmsteads. The Lisnabin example sits on a slight rise in gently undulating pasture, with higher ground closing in to the east and south but open views across the landscape in other directions. A pond lies about 95 metres to the southeast. The monument measures approximately 61 metres north to south and 54 metres east to west, enclosed by an earthen bank and an external fosse, the fosse being the wide, steep-sided ditch that runs around the outside of the bank. It was recorded on the Ordnance Survey six-inch map of 1837 as a roughly circular earthwork, and appeared again on the revised 25-inch map of 1913, by which point a slight indentation was visible on the south-southwest side. By 1970, when the monument was formally described, the bank had been almost entirely reduced to a scarp on the south-southwest to west arc, with several gaps caused by modern disturbance. A large quarry hole had been cut into the scarp and extends into the south-southwest quadrant of the interior. A modern causeway crosses the fosse at the east-northeast. There are traces of a slight outer bank at the east and west, with two large stones resting on it at the west-southwest, and the most convincing original entrance gap sits at the south-southeast, though a wider gap at the north is also a candidate. The partial ring of trees visible from aerial photography gives the earthwork a quality that is at once domesticated and quietly persistent, holding its outline in the pasture after more than a millennium.