It consists of two concentric stone enclosures, one set inside the other, a form that earned it the label 'double fort' on Tim Robinson's celebrated 1977 map of the Burren. A cashel, to give the more familiar term, is a ringfort built from dry stone rather than earthen banks, and this one at Tullycommon doubles the formula: an inner roughly circular wall enclosing a space about 46 metres across, itself surrounded by a much larger outer enclosure measuring nearly 95 metres at its widest. Between the two rings, the level ground is divided by radial walls, giving the whole structure the appearance of a loosely segmented wheel when seen from above.

The antiquarian Thomas Johnson Westropp visited and described the site in 1905, by which point it was already considerably deteriorated. He noted that the inner wall had been levelled to within about 1.2 metres of the ground at its highest, and he read this thinness and rough construction as signs of relatively late work. He recorded an east-facing entrance passage about 1.75 metres wide, with a substantial lintel stone lying nearby, measuring roughly 1.83 metres long. He also observed that the outer wall to the north-west still stood to around 2.4 metres and compared its coarse slab masonry directly to the outer ring of Cahercommaun, the well-known triple-walled cashel a few kilometres away. Since Westropp's visit, further deterioration has continued: the east-facing entrance he described is no longer clearly identifiable, inner facing stones have been robbed out or buried under collapsed rubble across much of the inner enclosure, and a later field wall has been built directly on the foundations of the outer enclosure wall along one stretch. Inside the inner enclosure, the remains of a hut site and a possible house can still be traced against the western wall. A separate cashel stands about 105 metres to the north-east, suggesting this corner of Tullycommon was once a place of some organised activity rather than an isolated fortification.