The interior of the rath at Carrowkilleen drops from its centre down to its eastern perimeter, faithfully following the natural fall of the ridge on which it sits. This is not a ruin dramatically asserting itself on a hilltop. It is a partly levelled oval earthwork, roughly 50 metres east to west and just over 61 metres across, occupying almost the full width of a narrow rectangular field before the ground opens out into a flat valley of damp pasture below.

A rath is an early medieval enclosure, typically of the first millennium AD, formed by a raised earthen bank and sometimes a surrounding ditch, or fosse, and used as a farmstead or settlement. At Carrowkilleen, the bank survives unevenly around the circuit. The south-western to north-western arc shows as a broad, gently raised strip, still retaining a slight internal lip. The northern arc is lower and more subdued, while the north-eastern to south-eastern section survives most clearly as a scarp cut into the slope itself, rising to about 1.4 metres on the exterior. The southern arc has largely disappeared. A fosse, roughly two metres wide and now only about 0.4 metres deep, runs along the south-western to western side of the bank but cannot be traced further around the enclosure. It is uncertain whether this ditch was dug when the rath was first constructed or whether it reflects later agricultural activity on the same ground. A relict field bank, now barely readable at ground level, extends westward from the northern end of the fosse, complicating the picture further.

Inside the enclosure, parallel cultivation ridges run east to west across the sloping interior and continue into the surrounding field. They clearly belong to a later period of agricultural use, laid down after the rath had ceased to function as an enclosure. A drystone wall, of the kind used to mark field boundaries and property lines across rural Connacht, cuts across the southern edge of the site, another layer of land use pressing into an already layered place.