A cashel is a ringfort enclosed by stone rather than an earthen bank, and this one survives as a slightly raised oval, roughly 26 metres north to south and 22 metres east to west. Along the southern, western, and northern arc, the enclosing wall has collapsed into a spread of rubble, between three and six metres wide but barely ten centimetres high in places, punctuated by some large upright boulders still holding their original position. The rest of the perimeter has been folded into the field boundary beside it, and the original entrance has been lost entirely.

Ringforts were built across Ireland primarily during the early medieval period, roughly from the fifth to the twelfth century, and served as enclosed farmsteads for individual families or small communities. Stone-built examples like this one are more common in areas where good building stone was readily available, and Sligo, with its limestone geology, produced many such sites. What survives at Carrownamaddoo is not dramatic in scale, but the low rise it occupies and the scrubby thicket that has grown up around it have, in a roundabout way, helped preserve what remains. The vegetation that obscures the site has also discouraged the kind of systematic stone-robbing that has erased so many comparable enclosures across the Irish countryside.