What survives at Carrowreagh, sitting on a gentle rise in County Mayo's rolling pasture, is a structure that is complete on one side and all but erased on the other, the northern half levelled to the point where it can only be detected as a faint undulation in the ground. That asymmetry is what makes it quietly arresting: enough remains to read the original design, but the erasure is just as legible as the earthwork itself.

A rath is a ringfort of earthen construction, typically dating from the early medieval period and used as a farmstead enclosure for a family of some local standing. The Carrowreagh example was roughly circular, measuring approximately 29 metres on its northeast to southwest axis and 27 metres across. On the surviving southern half, the anatomy is still reasonably clear: an earthen bank up to 4.8 metres wide, fronted by a fosse (a defensive ditch, 2.3 metres wide), which is itself backed by a low counterscarp bank of earth and stone. The counterscarp varies considerably; it is more substantial on the western side, reaching 2.5 metres in width, and becomes low and relatively insubstantial along the southeastern arc. The rath was positioned deliberately on a natural rise, which gave the interior a slightly elevated and level quality, and the views open most extensively to the southwest. The original entrance was on the south-southeast, marked by a narrow gap of about 1.8 metres in the bank, with traces of a causeway crossing the fosse at roughly 2 metres wide. Later agricultural activity has left its own marks: two field walls cut across the southern interior at right angles to each other, and one of them clips the inner face of the bank on the western side, a reminder that for most of the past millennium this monument has simply been farmland to work around.