The crop fills the interior so completely that the site could easily be passed off as ordinary farmland, and in practical terms it mostly is, which makes the archaeology quietly remarkable rather than obviously dramatic.

The earthwork is a rath, the Irish term for a ringfort, a type of enclosed settlement that was widespread across Ireland during the early medieval period, roughly between the fifth and twelfth centuries. Thousands survive in various conditions across the country, ranging from well-preserved earthen banks to barely legible cropmarks. This one at Ardkilleen survives as a roughly circular area, about 33 metres north to south and 32.5 metres east to west, enclosed by a low earthen bank that now stands only around 0.2 metres high. On the north-north-west to south-west arc, the outer edge of the enclosure still shows a silted-up fosse, the shallow ditch that would originally have reinforced the bank as a boundary or defensive feature. On the opposite arc, a slight scarp takes the place of the fosse. Atop the bank itself, a stone wall has been built at some point, along with a dump of field clearance stones, the accumulated debris of generations of farmers turning the surrounding ground for cultivation. The result is a site that has been continuously absorbed into agricultural use, each layer of farming activity pressing down a little further on what lies beneath.