The enclosure at Lisglassan measures thirty-eight metres across in both directions, which is to say it is almost exactly circular, a degree of precision that was clearly intentional rather than accidental. What makes it quietly strange is not any dramatic elevation or commanding view, but rather the opposite: it occupies a slight south-east-facing slope in an otherwise unremarkable setting, as though whoever constructed it was less interested in visibility than in defining and enclosing a particular patch of ground.

This kind of earthwork is broadly understood as a ringfort, a type of enclosed settlement built in Ireland predominantly during the early medieval period, roughly between the fifth and twelfth centuries. Thousands survive across the country in various states of preservation, though many have been levelled by agriculture over the centuries. At Lisglassan, the defining feature is an overgrown earthen bank with an external height of around two and a half metres on the south-western side, reinforced on the outside by the remains of a fosse, which is simply a ditch, cut into the ground to provide material for the bank and to add an extra barrier. The fosse survives in partial form, running from the east-south-east around through the west to the north-north-east. There appear to have been several points of entry, but three of the current openings are modern, probably widened or created for agricultural use. The southern entrance, just over two metres wide at the base, is considered the likely original, and it too now sees regular use by farm machinery, which says something about the way these ancient spaces are quietly absorbed into the working rhythms of the Irish countryside.