It is easy to miss: the bank that once enclosed the site stands only about half a metre above the interior ground level in places, and the defensive ditch, or fosse, that typically accompanies this kind of monument has either silted in or was never cut deeply enough to survive at the surface. What remains is a roughly circular enclosure, measuring around 24 metres east to west and 21.5 metres north to south, its perimeter defined by a bank of earth and stone about 4.3 metres wide.

This type of monument is known as a rath, the most common form of ringfort in Ireland, built during the early medieval period roughly between the 5th and 12th centuries. Raths served as enclosed farmsteads for a single family or small community, the bank providing a boundary as much social and legal as it was defensive. The Castletown example preserves a gap 3.1 metres wide on the eastern side of the bank, which is understood to be the position of the original entrance, a detail that corresponds with the common early medieval preference for east-facing openings. Along the east-north-east section, the bank has been removed and only a low external scarp remains, suggesting later disturbance or deliberate quarrying of the material. A small quarry pit sits just outside the bank at the north-west, which may be related to this kind of activity. Particularly interesting is the presence of a midden, essentially a deposit of domestic refuse, located just north-east of the centre of the interior. Middens on ringfort sites can contain animal bone, shell, and occasionally charcoal or other organic material that, when analysed, can shed light on the diet and daily life of the people who once lived within the enclosure.