Souterrains, typically built from dry-laid stone and roofed with large lintels, were used variously for storage, refuge, and purposes that archaeologists still debate. That one exists on Inis Gluaire is not entirely surprising; the island has a long association with early Christian settlement and is traditionally linked with Saint Brendan, who is said to have founded a monastery there. What is quietly remarkable is simply the fact of it, an engineered underground structure on a small Atlantic island, representing a level of organised habitation that tends to get overshadowed by the island's more legendary associations.

Inis Gluaire, sometimes anglicised as Inishglora, sits in Broadhaven Bay and is uninhabited today, though it preserves the remains of early ecclesiastical buildings alongside this souterrain. The island is perhaps best known in early Irish literature as the resting place of the Children of Lir, the figures from the mythological cycle who were said to have spent centuries transformed into swans before finding their final rest there. The co-existence of mythological resonance and datable archaeological remains, early stonework, underground passages, and monastic enclosures, makes the island an unusually layered site even by the standards of the Irish west coast.