The ringfort at Carrownaculla sits on a gradual north-west-facing slope, and its roughly circular outline, some 33 metres north to south and just under 30 metres east to west, is defined not by any dramatic earthwork but by a low scarp that barely announces itself above the surrounding ground. A short stretch of drystone wall caps the scarp at the south-south-east, and there are two areas where the bank dips low enough that an original entrance might once have been, though neither is clear enough to say so with any confidence.

A rath is an early medieval enclosed settlement, typically of the first millennium AD, in which a bank and ditch marked the boundary of a farmstead. Here the enclosing element is earthen rather than monumental, but the site carries an additional curiosity. Running through the interior on a north-west to south-east axis is a low linear rise, just wide enough and regular enough to suggest it follows the course of a souterrain beneath. A souterrain is an underground stone-lined passage, often associated with ringforts, used variously for storage, refuge, or ventilation. The slight drop in ground level from the south-west half of the interior to the north-east half seems to reflect this buried feature running beneath the surface. Around the outside of the rath, a drystone wall encircles the whole structure, but the gap between it and the scarp varies from under two metres at the north to nearly four metres on the east and south sides, and the consensus is that this outer wall belongs to a later phase of land management rather than to the original fort. Linear field walls radiate outward from it to the north, north-east, south, and south-west, and two of these, at north-east and south-west, appear to have flanked a trackway that once ran around the south-east arc of the rath, threading through the gap between the fort's own boundary and the encircling field wall. The landscape has been rearranged many times since the rath was built, but older routes and boundaries have a way of persisting, absorbed into later patterns without quite disappearing.