The rath at Reenogrena sits in level pasture on the lip of a coastal cliff, a detail that immediately sets it apart from the majority of Ireland's ringforts, which typically occupy inland rises or gentle slopes. The southwestern portion of its interior has been truncated where the cliff edge has eaten into it, leaving the enclosure open to the drop below.

A ringfort, or rath, is the most common monument type in the Irish countryside, a circular area enclosed by one or more earthen banks with an external fosse, or ditch, used as a defended farmstead during the early medieval period, roughly the fifth to twelfth centuries. This example is nearly circular, measuring 26 metres north to south and just over 26.7 metres east to west. Its bank survives to a height of 1.2 metres along the western to southern arc, and the external fosse, running from west to east, still reaches a depth of 0.8 metres. There are two breaks in the bank, one to the east at 2 metres wide and another to the north-northwest at the same width, likely original entrances. At some later stage the interior was put to a second use, as a burial ground, a repurposing that was not uncommon in Ireland, where the enclosing banks of an old rath offered a ready-made boundary for a small community cemetery, often informal and long predating any official parish record.