The rath at Doonmadden sits on a naturally occurring elevation within undulating pasture, with the ground falling gently away towards a stream roughly forty metres to the east. That combination, a slight height advantage and proximity to water, is exactly the kind of site that early medieval farming families in Ireland selected when building a ringfort, the circular enclosed settlements that were once the dominant form of rural habitation across the country, dating roughly from the fifth to the twelfth centuries.

The enclosure itself is nearly circular, measuring approximately 24 metres across its widest axis. Its bank, built from earth and stone and reaching an external height of around 1.6 metres on the north-west side, would once have formed a complete ring around the interior. Today only the western and north-western sections remain properly upstanding; elsewhere the bank has been worn down to a scarp, a sloped face in the ground rather than a raised wall of material. At the outer foot of the bank on the west side, there are traces of what may be a fosse, a defensive ditch, roughly 3.5 metres wide. Where the original entrance once broke through the bank, no clear evidence survives.