Eeragh Lighthouse, An tOileán Iarthach [Rock Island], Co. Galway

The design is not unusual for lighthouses of its era, but the flare is worth pausing on: it gave the structure a broader footprint to resist wind and wave without adding unnecessary height, while the glass-sided lantern and metal roof at the top let the light sweep out across the sea lanes that pass this notoriously exposed stretch of coast. A walkway rings the lantern, edged with a safety rail, presumably for the keepers who once climbed up to trim wicks and polish lenses through the night.

The lighthouse was commissioned in 1857, at a time when the west coast of Ireland was being steadily fitted with towers to guide shipping around its islands and headlands. Eeragh's job was to mark the western approach to Árainn, a stretch of water where a mariner unfamiliar with the shoreline could come to grief quickly. The building was never meant to stand alone: semi-detached keepers' houses sit just to the south, their pitched slate roofs and rendered chimneystacks giving the whole group a domestic, almost village-like character against the bare landscape. For over a century the arrangement depended on human presence, keepers living alongside the light they tended, watching the weather and the sea as much as the lamp itself.

That reliance on people ended in the twenty-first century. On 27 November 2006, the original light was replaced with a solar powered unit, a change that also reduced its range to 18 nautical miles. It is a quiet marker of how lighthouse keeping across Ireland moved from a manned, round-the-clock occupation to an automated, sun-fed process needing no one on site at all. The tower and its attendant houses remain as a set piece from that earlier working arrangement, the architecture of the buildings still legible even though their original purpose, in the fullest sense, has passed into automation.