Inishgort Lighthouse, Inishgort Island, Co. Mayo

Inishgort's tower does exactly this, its slate-hung sides battered gently from a granite plinth to a cast-iron railed gallery, so that the whole structure reads as a single tapering gesture rather than a stack of storeys. That silhouette, along with the curvilinear ironwork looping around the lantern, is no accident of a local builder's whim. It belongs to a recognisable family of early nineteenth-century Irish lighthouses, and once you know what to look for, the resemblance to towers hundreds of kilometres away becomes hard to unsee.

The lighthouse was built between 1827 and 1828, standing on its own outcrop and still recorded as functioning a decade later in 1838. It was designed by George Halpin Senior, who held the post of Inspector of Works and Lighthouses for the Ballast Board from 1810 until his death in 1854, a role that made him responsible for much of the lighthouse building programme around the Irish coast in that period. His hand can be traced in the near-identical treatment of towers at Kilcredaun in County Clare, completed in 1824, and at Greenore in County Louth, built between 1828 and 1830; the same tapering profile, the same confidence in cut granite paired with limewashed slate hanging. At Inishgort the granite does more than decorate. The plinth is chamfered, the corbels supporting the walkway are finished with a thumbnail bead, and the base beneath the lantern is built up in dressed ashlar, all before the ironwork takes over to carry the gallery railings around the light itself.

Inside, the practical geometry of a working lighthouse survives largely intact: a cut-granite spiral staircase winds upward, its wrought-iron balusters carrying a matching wrought-iron banister, a small domestic detail in an otherwise utilitarian structure. The window openings, square-headed with granite sills and concealed dressings, hold timber sash windows divided two-over-two, a modest touch of ordinary house-building grafted onto a maritime tower. Approached by a short flight of steps to its square-headed door, the building sits within its own grounds on the outcrop, isolated enough that its engineering, rather than any surrounding town or harbour, remains the whole of the story.