The earthwork measures roughly 46 metres east to west and 42 metres north to south, defined by a scarp only about 0.4 metres high and a shallow external fosse, the ditch that once reinforced the boundary. A possible entrance faces to the north-west. Modest by any measure, yet the form is unmistakable to anyone who knows what they are looking at.

This is a rath, the Irish term for a ringfort, the most common monument type in the Irish landscape. Ringforts were typically enclosed farmsteads of the early medieval period, roughly 500 to 1200 AD, where a family lived, kept livestock, and marked out their territory with a bank and ditch. What makes Lisnagoorneen slightly unusual is the detail recorded on the 1842 Ordnance Survey six-inch map, which shows not only the main circular enclosure of around 40 metres in diameter but a smaller concentric enclosure, about 8 metres across, at its centre. That inner feature, already faint enough by the mid-nineteenth century to be rendered only in hachures, the cartographic shorthand of shading used to suggest raised ground, had apparently softened further by the time the 1935 Ordnance Survey revision was made, when the map records only a single raised circular area. Whatever structure or feature that inner ring once enclosed, it left no obvious trace above ground by the twentieth century.