What remains is still legible in the landscape: two concentric earthen banks separated by a fosse, the ditch between them, running along the eastern and southern arcs. The outer bank stands up to 0.8 metres above the surrounding ground on its exterior face, while the inner bank is lower and broader. The interior, slightly raised on its northern side to compensate for the natural downslope of the hillside, sits in pasture, though the north-western quadrant has been swallowed by overgrowth.

Ringforts, also called raths, were the most common form of enclosed farmstead in early medieval Ireland, typically dating from roughly the fifth to the twelfth century. They were built by farming families as a combination of domestic enclosure and livestock protection, and the double-bank arrangement at Knockasarnet would have signalled a degree of status or security above the basic single-bank type. More unusual is the souterrain within the interior, an underground stone-lined passage of the kind frequently found beneath ringforts and used for storage or, in moments of danger, as a refuge. A linear feature running on a north-west to south-east axis, abutting the inner face of the inner bank to the east, may be structurally connected to this souterrain, though its precise function is unclear. A possible entrance opens to the south, the conventional orientation for such sites. The landowner noted that the interior was cleared during the 1990s, when a house was constructed immediately to the east of the rath. About 70 metres to the west lies a fulacht fia, a type of burnt mound associated with outdoor cooking or possibly bathing, and dating generally to the Bronze Age. Its proximity suggests the area was in use across a very long span of prehistory and early history.