The rath at Coolagh measures roughly 35 metres on its longer axis and 26 metres across, a modest but coherent double-banked enclosure with a fosse, the term for the ditch cut between the two banks, still legible in the ground. What catches the attention is the southern gap, about 3.3 metres wide, which appears to be the original entrance, the point where people and animals passed in and out of a settlement that was already ancient before the Normans arrived in Connacht.

Raths, also called ringforts, are among the most common archaeological monuments in Ireland, with tens of thousands recorded across the country. Most date to the early medieval period, roughly the fifth to the twelfth century, and functioned as enclosed farmsteads, the bank and fosse serving less as military defences than as boundaries keeping livestock in and wolves or neighbours out. The Coolagh example follows the standard pattern but preserves a few details worth noting. The inner bank runs continuously around the perimeter, though it is now heavily overgrown with hawthorn, a tree so frequently associated with ringforts in Irish folklore that it was long considered unlucky to cut one down. The fosse and outer bank have fared less well on the eastern side, and the north-eastern quadrant of the interior has been disturbed by quarrying at some point, removing whatever archaeology might have lain beneath that section. More intriguing is a small subcircular depression near the centre, roughly 3.5 by 2.5 metres, enclosed by its own low earthen bank. Features like this are sometimes interpreted as the footprint of a structure within the enclosure, though without excavation it is impossible to say more.