This one in Ballyadeen, County Cork, offers no such visible drama at ground level. What marks it out is that it exists, for most purposes, only from the air, its oval outline roughly fifty metres across on a north-northeast to south-southwest axis, legible only as a cropmark on flat grassland tucked into the north-eastern corner of a field.

A cropmark forms when buried features, such as a filled-in fosse or ditch, affect the growth of crops or grass above them. Soil that has accumulated in an ancient ditch tends to retain more moisture and nutrients, producing a slightly lusher, greener strip that shows up clearly in aerial or satellite imagery during dry spells. In this case, the feature is a large fosse, the term for a substantial defensive or boundary ditch, tracing out an oval enclosure that had gone entirely unrecorded until Jean-Charles Caillére spotted it while examining Bing Maps satellite imagery. The find was subsequently confirmed through lidar, a remote-sensing technique that uses laser pulses to build detailed elevation models of the ground surface, which can reveal subtle traces of buried or overgrown features invisible to the naked eye. No excavation or dating has been recorded for the site, so what the enclosure was built for, and by whom, remains open. Oval enclosures of this scale in Ireland are generally associated with early medieval settlement or ceremonial use, but without further investigation that remains inference rather than fact.