Roughly circular and about 28 metres across, it sits on a gentle rise amid undulating, waterlogged pasture, its edges defined by a shallow scarp a few metres wide. The southern side has been largely levelled, probably by centuries of agricultural activity, but enough of the form survives to read clearly as a deliberate, man-made shape in the landscape.

A rath is an earthen ringfort, the most common monument type in early medieval Ireland, typically dating from roughly the sixth to the tenth century. These enclosures functioned as enclosed farmsteads, with the surrounding bank and ditch offering a degree of protection for a family, their livestock, and their stores. The Gortnaboul example was already being recorded cartographically by 1916, when it appeared hachured, meaning marked with short lines indicating a raised feature, on the Ordnance Survey six-inch map of that year. Later formal surveys classified it somewhat cautiously as an enclosure before it was properly identified as a rath. The interior today is level and shows no visible surface features, meaning whatever structures once stood inside have left no trace above ground.

What is quietly telling about this particular site is its setting. The choice of a gentle rise within marshy ground was deliberate; such a position offered natural drainage, a degree of defensive advantage from the surrounding wet terrain, and clear views across the landscape. That logic, repeated across thousands of similar sites throughout Ireland, is easy to overlook when the monument itself is so modest in scale. At Gortnaboul, the marsh and the slight elevation between them do much of the explaining.