Two farmhouses sit facing each other across a rural road in County Kildare, separated by yards and outbuildings, apparently unaware that they occupy the interior of a prehistoric enclosure roughly the size of a large country estate. The structure that surrounds them is so subtle as to be almost entirely invisible from the ground, yet from the air it resolves into something remarkable: a near-circular area approximately 300 metres north to south and 260 metres east to west, one of the larger enclosures of its type recorded in the county.

The enclosure came to light through aerial photography carried out in 1968 under the Cambridge University Committee for Aerial Photography programme, when cropmarks, the differential growth patterns in vegetation that reveal buried features beneath a field's surface, traced a curving line along the northern and north-eastern arc of the site. That line is continued to the south-west not by any ancient earthwork but by a modern field boundary, which has effectively inherited the circuit of the original monument without anyone necessarily planning it that way. Where the boundary survives in older form, it takes the shape of a hedged earthen bank, between 1.8 and 2.5 metres wide, with an internal height of around half a metre and an external height of nearly two metres, fronted by a fosse, a ditch or external trench, some 2.6 metres wide and 1.3 metres deep, now recut and functioning as a field drain. A gap of about 4.3 metres on the southern side, accompanied by a small bridge just under four metres wide, may preserve the location of the original entrance. Immediately to the south, a rath (a type of enclosed farmstead common in early medieval Ireland, typically defined by one or more earthen banks) and two further enclosures run in a south-easterly line, suggesting this part of Ballynagappagh was a focus of some activity over a long period.

The enclosure sits on a long, gently south-facing slope amid mixed tillage and pasture, and the working farmsteads within it are still very much in use. The earthen bank is best appreciated along the south-western stretch where the hedged field boundary follows the ancient line most clearly, though there is no formal access and the monument announces itself only to those who already know what they are looking for.