This one in Pollaweela, on the southern bank of the Robe River in County Mayo, offers nothing to the naked eye at ground level. Walk the level pasture here and you would have no reason to pause. The enclosure exists, as far as anyone can currently tell, only from the air.

Aerial photography revealed a cropmark outlining a polygonal enclosure, roughly 20 metres across on its northwest to southeast axis and approximately 40 metres on its northeast to southwest axis. Cropmarks appear when buried features, walls, ditches, or banks alter how vegetation grows above them. In dry conditions especially, grass or crops over a buried ditch tend to stay greener longer, while those over a buried wall may brown more quickly, tracing the outlines of vanished structures in patterns only visible from altitude. The shape recorded here, polygonal rather than the more common circular or sub-circular form, is itself slightly unusual among enclosures of this type. No excavation or further survey appears to have established a date or function for the feature, and without that, its original purpose remains open.