It is a detail easy to miss, yet it is the kind of thing that rewards a careful eye: a faint hollow near the western interior of a ringfort, noted decades ago and not fully explained since. Ringforts, known in Irish as raths, were enclosed farmsteads typical of the early medieval period, built from raised earthen banks rather than stone, and used to define and defend a household's space against livestock theft and low-level raiding.

The enclosure at Lisnageer is oval in plan, measuring roughly 36 metres north to south and 30 metres east to west on its interior, which places it comfortably within the mid-sized range for earthwork enclosures of this type. It is surrounded by a substantial earthen bank, though the section running from the east-northeast to the north-northeast has suffered considerably over time. Beyond the bank runs a wide, deep fosse, the ditch that would once have added a meaningful obstacle to the perimeter, extending around the western and northern and southern sides of the site. An Office of Public Works survey carried out in 1969 recorded that the original entrance lay at the east-northeast, a common orientation for ringforts, where the morning light and the direction of approach would have been practical considerations. That same survey noted the curious depression inside the bank to the west, which may represent a filled-in souterrain, a collapsed storage pit, or simply a feature whose function has been lost to time.

The site is now overgrown, which makes any close inspection a matter of pushing through rather than strolling past. The earthworks are legible enough in outline, but the finer details of the interior are obscured by scrub and long grass. For anyone with an interest in early Irish settlement patterns, the combination of the surviving fosse and the ghostly interior hollow gives the site a quiet complexity that a tidier, more visited monument might not offer.