On the Ordnance Survey's six-inch maps of 1842 and again on the Cassini edition of 1920, the townland boundary between Fahee and Tullycommon takes a sharp, deliberate detour to the south and west, tracing around something that the mapmakers never bothered to mark. That something is a subcircular stone enclosure sitting in a slight hollow near the top of an exposed ridge above the 600-foot contour, surrounded by a multiperiod field system whose boundaries have been rearranged, generation after generation, to accommodate it.

A cashel is a type of ringfort defined by a stone wall rather than an earthen bank, and this one in Fahee retains enough of its structure to read clearly on the ground. The enclosing wall measures roughly 16 metres north to south and 14 metres east to west internally, with the best-preserved section at the north-north-east, where a double-faced wall still stands about half a metre high and just over a metre wide. The outer facing stones here lean noticeably inward toward the south-south-east, a sign of slow, long-term movement. Elsewhere the wall has spread and softened into a stony bank between two and five metres wide. A later field wall was laid directly over the bank on its northern arc, which is partly why the site went unrecorded on the early OS maps despite the boundary wall's conspicuous avoidance of it. Satellite imagery has since picked out grass-covered walls extending outward from the cashel at the north-north-east and south, suggesting ancillary structures, and a possible second enclosure sits about 50 metres to the south-south-east. The site was identified as a potential monument through aerial photography and formally listed in the Record of Monuments and Places in 1996.