A midden, in archaeological terms, is essentially a rubbish deposit, the accumulated debris of meals and daily life, and this one had been quietly sealed beneath layers of wall collapse and abandonment for centuries before anyone thought to look.

The midden came to light during excavations of the western half of Dún Aonghasa's inner enclosure, when the debris overlying Structure 2 was carefully removed. What emerged extended across the ruined foundations of an earlier building, Structure 5, meaning it post-dates that structure entirely. The handful of finds retrieved, a sherd of worn pottery and two used cobbles, does not resolve the question of precisely when the deposit formed. It could belong to the early medieval period, when Structure 2 appears to have been in use, or it could represent a much later episode of occupation, people sheltering within or near the old walls long after the fort's main phase of life had ended. That ambiguity is itself significant: it suggests the enclosure continued to attract human activity across a long and uneven span of time, even as its grander architectural elements fell into ruin around whoever was eating limpets in the corner.