Grass-covered, flat-topped, barely forty centimetres high and roughly three and a half metres across at its base, it tapers to a top only a metre wide. It looks, at first, like a natural hump in the ground. It is almost certainly a midden, which is to say a prehistoric rubbish heap, the kind of deposit where the accumulated domestic waste of past inhabitants, food remains, broken tools, ash, bone, shell, slowly consolidates into a durable earthen feature that outlasts almost everything else about the lives of the people who created it.

The mound sits within a rath, the Irish term for a roughly circular earthwork enclosure, typically defined by a bank and ditch, that served as a farmstead during the early medieval period. Raths are common across Ireland, numbering in the tens of thousands, but their interiors are less frequently examined in detail, and features like this one can go largely unremarked. The Castletown example is modest in every dimension, yet its position within the enclosed space raises quiet questions about the daily rhythms of whoever occupied the site. Middens, because of what they contain, can be among the most informative deposits an archaeologist encounters, though there is no indication that this one has been excavated or that its contents have been analysed.