This is a bivallate rath, meaning a ringfort enclosed not by one but by two concentric banks and their accompanying ditches, and the scale of it is quietly impressive. The outer diameter runs to nearly 66 metres north to south, while the interior, where people once lived and kept their animals, measures around 24 by 27 metres across.

Ringforts of this kind were the most common form of rural settlement in early medieval Ireland, built roughly between the fifth and twelfth centuries and serving as farmsteads for extended family groups. The double-bank version, less common than the single-ringed type, is generally associated with higher-status occupants, the extra circuit of earthwork representing additional effort, additional enclosure, and perhaps additional prestige. At Coolnaleen the structure sits on a rise that slopes steeply east to west, and this gradient has shaped the earthwork in visible ways. The inner bank, which averages 7.2 metres in width and stands up to 3.6 metres on its outer face, is well preserved throughout. The outer bank is more variable; to the south, where the slope drops away sharply, it has been worn lower, but on the southern exterior it still climbs to between 2.6 and 6 metres, the hillside lending it an almost exaggerated height from below. The U-shaped ditches, or fosses, between and around the banks remain clearly defined in places, and the original entrance is still legible: a 4-metre-wide gap in the inner bank to the east, with a causeway crossing the fosse to a 3.4-metre opening in the outer ring. A secondary gap of about 2.2 metres survives to the west. That an entrance causeway should remain recognisable after so many centuries says something about how thoroughly the topography here has resisted disturbance.