No earthwork survives above ground, but for part of the year the outline of the enclosure reportedly declared itself through a high ring of yellow iris, known locally as "flaggers", whose roots had taken hold along the old earthen banks and refused to forget them.

The scholar T. J. Westropp recorded the site in 1909, when enough remained to measure. A ringfort, or rath, was a roughly circular enclosure used in early medieval Ireland typically as a farmstead or defended homestead, bounded by one or more earthen banks with external ditches. What Westropp found at Doon was modest even by the standards of such sites: a fosse, the external ditch, only nine feet wide and barely a foot deep, traces of an outer ring somewhere between six and eight feet thick, and a garth, the enclosed interior space, measuring fifty-four feet across. It was small, shallow, already fading. The yellow iris had taken the place of the bank, tracing its arc through the vegetation long after the earth itself had been disturbed or worn away.