It does not announce itself with height or drama. The enclosing bank, an earthen rim that makes this a univallate rath, meaning a ringfort with a single enclosing bank rather than multiple concentric ones, rises only between half a metre and one and a half metres above the surrounding ground on its outer face, and averages around eighty centimetres on the inside. It is wide rather than tall, softened by time into the pasture. What gives it away, if you are looking, is the shape: a roughly circular enclosure measuring thirty-one metres north to south and thirty-four metres east to west, sitting directly behind a small wooded area in low-lying farmland.

Ringforts of this type are among the most common archaeological monuments in Ireland, with tens of thousands recorded across the country. They date broadly to the early medieval period, roughly the fifth to twelfth centuries, and are thought to have served as enclosed farmsteads, the earthen bank and any timber palisade that once topped it offering a degree of protection for a household and its livestock. The Tullahennel example follows the typical form closely: a circular or near-circular enclosed area, a single earthen bank, and a gap that likely marks the original entrance. That gap, three metres wide and positioned to the south-east, is one of the more readable features on the ground. A fieldbank running along the southern side of the site has become integrated into the monument's edge over time, making it harder to distinguish the original boundaries cleanly.