Along the northern side, a natural meander scarp, the steep eroded face of a river bend, rises six metres and runs for fifty-eight metres, effectively replacing the need for any man-made earthwork along that stretch. The result is a large D-shaped enclosure, roughly eighty-five metres by sixty-two metres internally, that sits above the point where the Ferta river meets one of its tributaries on the Iveragh Peninsula in south Kerry.

A ringfort, or rath, is an enclosed farmstead of the early medieval period, typically dating from roughly the fifth to the twelfth century, in which a family and their livestock lived within a raised earthen bank and an outer ditch called a fosse. At Foilmore, the enclosing bank is composed largely of earth, averages about a metre in internal height, and drops nearly two metres down to the external fosse. That fosse is preserved intermittently, surviving best along the south-eastern and western sectors, where it averages three metres wide at its base. A three-metre gap on the east-north-east side may mark the original entrance. The bank has been modified over the years and is capped with modern stone walling along much of its eastern side, a common fate for earthworks that were gradually pressed into service as field boundaries. Inside, the north-western half of the enclosure preserves a more complex picture: a series of low, grass-grown, stony banks defines a rectangular area within which the foundations of at least one sub-circular hut survive, measuring six metres in maximum internal diameter. A stony mound nearby contains a notably high proportion of quartz, which is unusual enough to catch the eye. A second circular raised area, 1.15 metres high and roughly seven metres across, close to the north-western perimeter, may be the remains of a further hut. The detailed survey of these features was carried out by A. O'Sullivan and J. Sheehan as part of their archaeological survey of the Iveragh Peninsula, published by Cork University Press in 1996.