To the casual eye it might read as a slight rise in the ground, an irregularity in the grassland, but the geometry is deliberate and the engineering still legible.

This is a rath, the Irish term for a ringfort, the most common monument type surviving in the Irish countryside. Raths were typically enclosed farmsteads, home to a single family and their livestock during the early medieval period, roughly the fifth to twelfth centuries. The Glenreagh example is roughly circular, measuring thirty metres north to south and twenty-four metres east to west internally. It is defined by an earthen bank that rises half a metre above the interior ground surface and two metres above the exterior, giving it a considerably more imposing face when viewed from outside. Beyond the bank lies a fosse, a defensive ditch approximately five metres wide, which survives best in the southern sector, where it has been re-cut and pressed into service as a field boundary, a practical reuse that has paradoxically helped preserve it. A south-west entrance, 3.5 metres wide, is crossed by a ramped causeway over the fosse, the original point of passage still intact. The interior slopes noticeably downward toward the north, following the natural fall of the hillside rather than any levelled platform.

The site today is heavily overgrown, with trees and scrub colonising both the interior and the perimeter bank. That density of vegetation makes the earthworks harder to read from within, but approaching from the south, where the fosse is clearest and the outer bank at its tallest, the structure of the place becomes easier to appreciate.