It is the kind of place that rewards a second look, because at first glance it reads simply as a slight rise in the ground. Only when you begin to trace its outline does the deliberate geometry become clear: a roughly circular platform, approximately 38 metres across at its widest, defined by an earthen bank and a shallow external fosse, the trench dug around the outside of a ringfort to reinforce its enclosure.

Ringforts, known in Irish as raths when constructed from earth rather than stone, were the most common form of rural settlement in early medieval Ireland, typically dating from around the sixth to the twelfth centuries. They served as enclosed farmsteads, the bank and fosse forming a boundary that was as much a statement of social standing as a defensive measure. This example in Derrynagarragh has not fared especially well over the centuries. The bank has been levelled along its north-western to north-eastern arc and dug into on its south-south-eastern side. A possible entrance gap survives at the south-east, which is a common placement for ringfort entrances. Inside, the ground rises gently towards the centre and shows several slight depressions, most likely the scars of earlier digging into the interior. Ballyknock Bridge, which carries a crossing over the Yellow River some 90 metres to the north-east, marks the townland boundary with Ballybeg at that point, and Ballyknock House lies around 70 metres to the west.

The earthwork is set on its hillock with clear sightlines across the countryside in multiple directions, a positioning that would have been entirely intentional for whoever established the farmstead here well over a thousand years ago. The landscape has changed considerably around it, but the low profile of the rath persists, worn and partly dismantled, in the middle of what is now ordinary agricultural land.