Its first-floor doorway, reached originally by a retractable ladder, opens onto nothing but air; the only way in was to be hauled up, a design that speaks less to architectural whimsy than to a very specific kind of anxiety about who might be coming ashore.

The tower at Knockadoon was one of more than eighty signal stations erected by the British Board of Ordnance along the Irish coastline in the early years of the nineteenth century, forming a continuous chain from Dublin Bay clockwise all the way around to Malin Head in Donegal. The purpose was straightforward: to give advance warning of a French invasion fleet. Each station communicated with its neighbours using a naval signal post, relaying coded messages along the chain at speed. Knockadoon's nearest links were the station at Ballymacotter, roughly fifteen kilometres to the west-southwest, and the one at Ardmore in County Waterford, about thirteen kilometres to the east-northeast. The system was abandoned by the mid-1810s once the threat receded. The Knockadoon tower is built of roughly coursed rubble stone with lime render on the exterior, weather-slating still visible at the upper levels, and cut stone coping along the parapet. Red brick features in the machicolation above the doorway and in the small bartizans, which are corner turrets projecting from the rear elevation, each supported on corbels; whether this brick is original or reflects later repair is not certain. The threat the station was built to watch for never came, and the whole network was quietly stood down within a decade.

The site holds a second layer of history in close proximity. About thirty metres to the southeast sits a well-preserved Second World War reinforced concrete lookout post, and a recently restored "21 Eire" sign lies to the southwest, a marker placed during Irish neutrality to identify the country's coastline to aircraft overhead. Two separate moments of coastal vigilance, separated by over a century, share the same rough pasture above the water.