What makes this particular rath worth attention is not dramatic preservation but a small structural detail: attached to its western side is a subcircular annexe, a secondary enclosure roughly 39 metres across east to west, defined by its own scarp and fragmentary bank. Annexes of this kind are relatively uncommon additions to ringforts, and their function is still debated, with possibilities ranging from livestock penning to the accommodation of a dependent household.

The main enclosure is about 60 metres in diameter, and it follows the classic form of a rath, the Irish term for a ringfort defined by earthen banks and a fosse, the shallow ditch between them that provided the material for the banks themselves. These were the farmsteads of early medieval Ireland, occupied roughly between the fifth and twelfth centuries, and several thousand survive across the country in varying states of repair. At Knockavanny, the inner bank has been largely reduced to a scarp, a slope in the ground rather than a standing mound, while the outer bank survives only on the western side. An entrance gap is still visible to the east, which was the most common orientation for ringfort entrances. Later agricultural activity has left its mark too: a field wall cuts across the monument at the south-west and north-west, a reminder that for much of the post-medieval period these earthworks were simply inconvenient obstacles in working farmland rather than protected monuments.