No one is certain who built it or when. That ambiguity alone sets it apart from the more celebrated structures on the island, and makes it worth a closer look.

What survives is a subrectangular outline, roughly 8.2 metres long and 4.6 metres wide, formed from irregular boulders arranged in inner and outer wall facings. The double-faced construction suggests a proper wall with a rubble core between the two skins, a technique common across many centuries and many building traditions in the west of Ireland. At the western end, traces of an internal wall division are still faintly visible. The structure is poorly preserved, which is part of why dating it has proved difficult. High Island, known in Irish as Ardoileán, is perhaps best known for its early medieval monastic remains, and it is tempting to read this building within that context, but the notes attached to it stop well short of any such claim. Its date remains genuinely indeterminate.