To the west, the ground gives way to a turlough, one of those seasonally flooding limestone lakes particular to the west of Ireland, which fill and empty according to the water table rather than rainfall alone. Sitting on the hill's summit, the rath would once have commanded a clear view over this shifting, unreliable body of water, a presence that must have shaped how the site was chosen in the first place.

The rath itself, a type of enclosed farmstead typically built during the early medieval period, roughly between the fifth and twelfth centuries, is subcircular in plan and modest in scale, measuring approximately 31 metres on its longer axis. Despite being poorly preserved, the underlying structure is still legible. Three concentric banks of earth and stone, now heavily grassed over, define the enclosure, along with a fosse, the ditch that would originally have separated the banks and added to the defensive depth of the site. A three-banked rath, sometimes called a trivallate rath, is comparatively uncommon; most examples have only one or two banks, and the additional circuit is generally thought to indicate higher social status or greater concern for security. At Cregboy, the innermost bank survives continuously around the circuit, while the fosse and middle bank are traceable from the south-east around through west to north-east. The outermost bank runs further down the slope, extending from the south-west and remaining visible as far as north. A narrow causewayed gap on the south-south-east side, just under two and a half metres wide, may represent the original entrance through the earthworks.