The enclosure measures roughly thirty metres across and is defined by an earthen bank about four metres wide, rising nearly a metre on the interior and slightly more on the outside. These proportions are modest but deliberate, the kind of boundary that once separated a farmstead and its inhabitants from the wider world.

A rath, as this type of ringfort is known in Irish, was the most common form of rural settlement in early medieval Ireland, typically dating from roughly the fifth to the twelfth century. Most were working farmsteads rather than fortifications in any military sense, enclosing a family's house, animals, and outbuildings within a raised bank and an outer ditch. At Coolbaun, the remnants of that outer ditch, called a fosse, are still faintly traceable on the south-west to north arc, and become waterlogged in places, which has likely helped preserve what little remains. The bank itself has been interrupted by cattle gaps cut through the south and south-south-east, and on the west-south-west side there is a slightly wider gap of around one and a half metres that may represent the original causeway entrance, the point where a raised pathway once crossed the fosse to reach the enclosed interior. Inside, the ground is level but now covered in overgrowth. Modern field boundaries press in from the north-east, south-east, and south-south-west, their lines butting directly against the ancient bank, suggesting the surrounding farmland has been continuously worked and subdivided around this older feature for generations.