What makes the position striking is less its height than its deliberateness. Whoever chose this spot could see in almost every direction, with the Dartry Mountains and the Ox Mountains both visible from the summit, and a deep valley falling away to the north-west. The enclosure itself is modest, a circular raised area roughly 25 metres across, but the choice of ground suggests that visibility, or at least the impression of command over the surrounding landscape, mattered a great deal to the people who built it.

Ringforts, sometimes called raths, are the most common type of early medieval monument in Ireland, typically dating from roughly the fifth to the twelfth century. They served as enclosed farmsteads, protecting family groups and their livestock rather than functioning as military fortifications in any grand sense. This example at Knocknashammer follows the standard pattern: a low bank, now degraded, running around the perimeter, with stones still visible where the earthwork has eroded. The bank measures about 3.7 metres wide and 1.2 metres high, and outside it runs a fosse, the shallow ditch that would have provided the material for the bank when it was first constructed. An entrance survives on the southern side, roughly 2.3 metres wide, and within the enclosure there are traces of a souterrain, an underground stone-lined passage or chamber that was typically used for storage or, in times of danger, as a place of temporary refuge. The interior of the enclosure rises very slightly at its centre, suggesting there may be further subsurface remains beneath the turf.