The enclosure at Thomondtown shows up not as a raised feature on the landscape but as a negative cropmark, meaning the circular outline becomes legible through differences in how crops grow over buried or disturbed soil. Negative cropmarks of this kind typically appear where a buried bank or wall impedes root growth and moisture retention, causing the vegetation above to ripen or stress slightly earlier than the surrounding crop. Satellite imagery captured on 4 July 2008 caught exactly this effect, outlining a near-perfect circle in a large arable field.

The enclosure is circular in plan with an external diameter of approximately 27 metres, defined by a low bank roughly 2.5 metres wide. No clear entrance gap has been identified through the bank, which is unusual and leaves the enclosure's original function open to interpretation. It sits about 813 metres south-east of the Gracedieu monument complex, a cluster of recorded archaeological features that suggests this part of north Dublin was a place of some sustained human activity. An unnamed stream runs west to east roughly 159 metres to the south, the kind of modest watercourse that often determined where people chose to settle or enclose ground in earlier centuries. The record was compiled by Tom Condit and uploaded in April 2021, placing it relatively recently into the formal archaeological inventory.

The enclosure is not signposted or marked in any way on the ground, and because it sits within an actively farmed arable field, access would depend on the season and the goodwill of the landowner. The cropmark is only legible from aerial or satellite vantage points, so a visit at ground level would likely reveal little more than a slight rise in the soil, if anything at all. Those interested in exploring the broader area would find the nearby Gracedieu complex, which encompasses multiple recorded monuments, a more rewarding starting point. The stream to the south and the gentle, open character of the landscape do at least give a sense of why this particular corner of Dublin might have attracted attention long before anyone thought to map it.