The rath that once occupied this ground is no longer visible at surface level, having been levelled in the 1960s, but its oval outline, roughly 60 metres from northeast to southwest and 40 metres from northwest to southeast, was clearly recorded on Ordnance Survey maps from both 1846 and 1895. A rath, sometimes called a ringfort, was a type of enclosed settlement widely used in Ireland from roughly the early medieval period, consisting of a raised earthen bank, or sometimes several concentric banks, encircling a domestic space. The one at Coolroe was a modest example, defined by a single bank, but it contained something more unusual: a souterrain.

A souterrain is an underground stone-lined passage or chamber, typically associated with ringforts, and thought to have served for storage, refuge, or both. The souterrain at Coolroe survives beneath the flattened field even though the enclosing earthwork around it does not. The rath itself can be traced back through two separate documentary threads. The 19th-century OS maps show its shape and approximate dimensions with reasonable precision. Then, decades later, it appears to have been noted in the 1940s through the Schools Manuscript collection, a nationwide project in which Irish schoolchildren recorded local folklore, placenames, and physical features of their areas, often capturing details of monuments that formal surveys had yet to document. The Coolroe entry described a circular rath with "one fence", a phrase that corresponds neatly with what the landowner later confirmed about a single surrounding bank. By the time that recollection was set down, the feature was already at risk; within a generation, the bank was gone.