The earthen bank enclosing it reaches up to 2.5 metres at its highest point, and the enclosed area measures roughly 30 metres across in both directions, making it a reasonably substantial example of its type.

This is a rath, the Irish term for a ringfort, the most common surviving monument type in the Irish countryside. Ringforts were typically enclosed farmsteads, built and occupied during the early medieval period, roughly between the fifth and twelfth centuries. They served as protected homesteads for farming families, with the enclosing bank and any associated ditch providing a degree of security for people and livestock. The Grenagh example retains some interior features that add a little texture to the site. A low L-shaped bank sits in the north-east quadrant of the interior, measuring about 11.6 metres along its longer axis, and a small raised platform, roughly 4 metres long, 3 metres wide, and just over half a metre high, occupies the south-east quadrant. Such internal features are not always preserved, and their presence here suggests the site has escaped the more thorough levelling that agricultural improvement brought to many comparable monuments across Cork and elsewhere. The trees, though a modern addition, have in their own way contributed to that preservation by discouraging further disturbance.