Somewhere on the open grassland of the Curragh, a circular pattern in the earth raises more questions than it answers. Spotted in a 1970 aerial photograph, the feature appears as a roughly circular area of approximately 100 metres in diameter, enclosed by two and intermittently three non-concentric fosses, that is, ditches dug into the ground forming a series of looping boundaries that do not share the same centre point. On the ground, it may be almost invisible to a casual walker; from the air, it resolves into something deliberate and ordered.

What it actually represents remains uncertain. The site may be a relatively modern construction rather than anything from the early medieval or prehistoric periods that produced so many of Ireland's enclosures and ringforts. The Curragh itself has long been defined by the thoroughbred horse industry, and the Kildare plain has been used for grazing, training, and racing for centuries. A functional enclosure associated with that industry, perhaps for containing or managing horses, is one plausible explanation, though none has been confirmed. The multiple non-concentric fosses give it a slightly unusual profile even by the standards of practical field enclosures, and no firm date or original purpose has been attached to it.