The site at Lisnashannagh is a ringfort, a type of enclosed farmstead or defended settlement built predominantly during the early medieval period in Ireland, roughly between the fifth and twelfth centuries. Thousands survive across the island, but each one repays attention on its own terms, and this one has several details worth pausing over.

The enclosure is subcircular in plan, measuring approximately 33 metres from west-northwest to east-southeast and 28 metres across the shorter axis. It sits as a raised platform, defined by an earthen bank whose outer face still stands around 2.2 metres high on the western side, even if the interior face has been worn down to little more than 0.3 metres. Around the outside of that bank runs a fosse, the water-filled or waterlogged ditch that would have added a further obstacle to any unwanted approach. At the west-northwest, the fosse retains a width of 2.5 metres at the top and drops roughly half a metre to its base. A field bank running from north to southeast bounds the site externally, overlapping the ancient enclosure with the more recent geometry of agricultural land division. The original entrance appears to have been on the eastern side, where a causeway crossing the fosse survives, 1.8 metres wide and raised 0.45 metres above the ditch floor, though this eastern gap has since been widened beyond its original form. On the opposite side, a large depression cuts through the bank at the west-southwest, measuring 8 metres by 4 metres and reaching a metre in depth; whether this represents a later breach, a deliberate secondary opening, or something else is not recorded.