A cashel is a ringfort built from dry-stone walling rather than earthen banks, and this particular example sits on a sheer rock face on its western side, which both anchored the structure and gave its builders a natural defensive advantage without additional labour.

The cashel at Gragan is roughly circular, measuring about 23.5 metres north to south and 22 metres east to west, with a wall some 2.5 metres wide that was faced on both its inner and outer surfaces. The outer face has survived considerably better, standing between one and 1.3 metres high for most of its circuit, and rising to nearly 2.5 metres where it sits directly on the western rock face. A probable entrance gap, around 3 metres wide, opens at the south-east. Two small rectangular stone-walled huts are built against the outside of the cashel wall, one to the east and one to the south-west; when the first Ordnance Survey mapped the area in 1842, both were recorded as roofed, meaning they were still in use or at least intact at that point. A curving earthen bank runs alongside the eastern hut, and a semicircular enclosure presses up against the cashel at the north. A later wall was added running from the west around to the north-east, evidence that the site continued to be modified and used well beyond its original construction. The whole complex sits within a multiperiod field system, indicating that the agricultural landscape around it was itself laid out, reworked, and reused over a long span of time. The two neighbouring cashels, one roughly 120 metres to the north and another about 90 metres to the south-south-east, reinforce the impression of a locality that was once considerably more densely settled than its present appearance of open pasture might suggest.