This ancient cashel, measuring 24.5 metres north to south and 22.5 metres east to west internally, sits roughly 40 to 50 metres north of a small tributary of the Milltown river. The stone fort, which may have included a souterrain, underwent significant modifications at an unknown later date, transforming it into part of a much larger defensive complex.

The cashel now occupies the northeastern corner of an extensive rectangular enclosure stretching 73.5 metres east to west and 44 metres north to south. The most striking features are two massive stone mounds, each nearly 3 metres high and standing 1.7 metres apart, marking where the southwestern section of the cashel wall once stood. These imposing ruins are believed to be the remains of a gate-house tower added during later fortifications. Historical accounts from the 19th century describe this gateway as 1.8 metres wide with walls 5.5 metres thick, complete with perforated stones for securing gates. Local tradition recorded in 1870 suggested the gateway was once arched or lintelled, flanked by guard chambers, with steps leading to the top of the wall still visible on the inner face.

Beyond the tower ruins, several other defensive features remain visible. A low bank extends westward from the southern mound for about 18.5 metres, ending at a circular structure roughly 3 metres in diameter, now reduced to a hollow stone mound. Against the inner face of the northern wall, a wedge-shaped structure measuring 9 metres at its widest point provides further evidence of the site’s complex defensive history. While the exact dates of these various modifications remain unknown, the layered ruins at Cahercullaun offer a tangible connection to Kerry’s long history of fortified settlements and the communities who continually adapted them to meet changing defensive needs.