A ringfort, or rath, was a roughly circular enclosure defined by an earthen bank and ditch, used during the early medieval period as a farmstead or high-status residence. This one is gone, its banks flattened at some point well before living memory, and the ground above it gives no visible sign that anything ever stood there.

What makes Rathculleen slightly more than just an absence is what turned up when the land was ploughed in around 1937. According to P. J. Hartnett, writing in 1939, tillage operations brought up large quantities of vitrified stone from the interior of the former fort, along with a rich black deposit found immediately to the south and south-east. Vitrified stone is material that has been subjected to intense heat until it partially fuses or glazes, which can indicate the collapse of a burning structure or the remnants of industrial activity such as metalworking. The black deposit, apparently organic and soil-like in character, was considered fertile enough that the landowners spread it across the adjacent fields as top-dressing. By the time Hartnett recorded the site, even the faintest traces of the bank were only barely discernible, suggesting a diameter of approximately two hundred feet, but those traces have since disappeared entirely. The archaeology, in effect, was redistributed across the surrounding farmland.