The structure is subrectangular, roughly twelve metres across, and sits on a north-west-facing slope in a field at the shoreline's edge. That orientation is worth pausing on: a north-west aspect offers little shelter from Atlantic weather, which raises the question of why someone chose to build here at all, and what kind of life was lived within walls that would have caught the full force of incoming gales.

The site is known as a hut site, a broad archaeological category used to describe the remains of a simple, usually single-roomed dwelling defined by a bank or low wall, often of earth and stone. Without excavation, it is difficult to date such structures precisely; they appear across Ireland from the early medieval period onwards, sometimes associated with seasonal grazing, sometimes with small farming settlements, sometimes with coastal activities such as fishing or kelp-gathering. At Crumlin, the defining bank is still visible, picked out on aerial photography, its roughly rectangular form suggesting a deliberately built space rather than a natural feature. The proximity to the sea, and the marginal, exposed position on the slope, fits a pattern seen elsewhere along the Irish coastline, where small communities or individual households occupied the land closest to the shore, working whatever the sea and the thin coastal soil could offer.