It is easy to walk past without registering what you are looking at, which is precisely what makes it worth slowing down for. This is a ringfort, the most common surviving monument type in the Irish countryside, a circular or near-circular enclosure defined by an earthen bank and shallow external ditch, known as a fosse, that once enclosed a farmstead and its outbuildings during the early medieval period.

The enclosure at Glenidan measures approximately 29 metres on its north-west to south-east axis and takes a sub-circular rather than perfectly round form. Its earthen bank is poorly preserved, broken in several places by disturbance gaps, and the fosse outside it is slight and narrow, suggesting centuries of agricultural activity have done their gradual work on the perimeter. The interior ground slopes from north-west to south-east, and faint traces of cultivation ridges survive within, hinting at land use that continued inside the enclosure long after its original function had been forgotten. The site was already old enough to be unremarkable when it was recorded as a circular enclosure on the 1837 edition of the Ordnance Survey six-inch map, that early and systematic effort to document the Irish landscape that incidentally preserved the outlines of countless monuments that might otherwise have gone unrecorded entirely.