The walls of this early nineteenth-century signal tower have collapsed to ground floor level, leaving a low limestone shell so reduced that its original purpose would be easy to miss entirely. Yet the site sits in open, unobstructed pasture with clear sightlines in every direction, and that quality of exposure is precisely the point. This was a watchtower built not for defence but for communication, one node in a coastal warning network designed to carry information across hundreds of miles of Irish coastline as fast as a signal flag could be read.

The tower was built, or at least begun, around 1804 to 1806 by the British Board of Ordnance, which constructed over eighty such stations in the opening decade of the nineteenth century. The context was the Napoleonic Wars and the very real fear of a French invasion fleet appearing off the Irish coast, a fear with recent precedent given the French landing at Killala Bay itself in 1798. The stations were linked by naval signal posts and formed a continuous chain running clockwise from Dublin Bay all the way around the coast to Malin Head in County Donegal. The Lenadoon tower appears never to have been completed; current thinking is that construction may have been abandoned mid-build and the intended station relocated to nearby Rathlee, about 1.7 kilometres to the south-east, where a finished signal tower still stands and whose upper levels are visible from this site. The upper walls of Lenadoon never rose above ground floor height, and the limestone rubble walls that survive reach only 3.48 metres. Enough remains, however, to read the intended layout: a shallow outward bulge in the south-east wall marks the chimney flue, a chute cuts steeply through the same wall, and joist holes in the south-west wall show where the timber floor structure was intended to sit. Roughly fourteen and a half metres to the west, a shallow oval depression in the ground is thought to be a lime kiln, a structure used to produce mortar during construction, and may have served this very building project before work was halted. The whole system was abandoned by the mid-1810s once the threat of French invasion had passed.

The site sits close to a shingle beach on the eastern shores of Killala Bay, with the remains of grassed-over rubble stone field walls still connecting to the tower at its north and south corners. A probable late medieval church and burial ground at Carrowmacbryan lies about 576 metres to the south-south-east, adding a further layer to a landscape that repays careful attention at ground level.