A roughly rectangular arrangement of stone, measuring seven metres by four, occupies the interior of the rath in a way that suggests it was once a structure of some kind, though precisely what that structure was remains an open question.

A rath is a circular or oval earthwork enclosure, typically of early medieval date, formed by one or more banks and ditches. They are common across Ireland, and were generally used as farmsteads or defended homesteads. What makes the Doonflin example worth pausing over is this internal feature: a subrectangular footprint of stone, modest in scale but deliberate in form. Whether it represents the remains of a building, a storage cell, or some other domestic or agricultural use, the stonework is enough to indicate that the space inside the rath was organised and used with some intention. Most rath interiors, when not disturbed by later farming, preserve traces of exactly this kind of activity, though many go unrecorded or are too eroded to read clearly. Here, at least, the outline survives.