The inner feature is oval to subrectangular in shape, measuring roughly 23 metres east to west and 13 metres north to south, and its interior sits approximately 0.4 metres below the surrounding exterior ground level. That slight but deliberate sunken quality, defined by an inward-facing scarp, a sloped earthen edge that drops toward the centre rather than rising away from it, suggests something purposefully constructed rather than the result of natural erosion or agricultural accident.

This inner enclosure occupies most of the northern half of a larger enclosure at the same site. Nested features of this kind are not uncommon in the Irish archaeological record, though their precise functions are often difficult to determine without excavation. The combination of a sunken interior and an enclosing scarp could point to any number of uses across a broad stretch of prehistory or the early medieval period, from stock management to ritual or domestic activity. What makes Carrownaknockan worth attention is the legibility of the arrangement itself, the way the two enclosures relate to one another spatially, with the inner feature claiming the majority of one half of its parent.