The tower itself, built around 1806 to a neat square plan of roughly 4.3 metres aside, was reportedly in reasonable condition until a lightning strike during a storm in the 1960s brought most of it down in a single event. The collapse was evidently violent enough to scatter stonework far to the east, where the ground drops away steeply into blanket bog. What survives upstanding is fragmentary: the north and east walls still show short sections of original lime render on their inner faces, and the north wall retains a central stone pillar that once divided two ground-floor windows. A square vertical drainage channel is cut into the north wall's east end. The south wall is gone entirely, though its footprint is still legible at ground level.

The tower was one of more than 80 signal stations built by the British Board of Ordnance along the Irish coastline in the first decade of the nineteenth century, forming a continuous chain from Dublin Bay clockwise around the coast to Malin Head in County Donegal. Their purpose was to relay warnings of any approaching French invasion fleet using naval signal posts, a system of flags and mechanical semaphore that could pass a message along the chain far faster than any messenger on horseback. The station at Cleggan Hill, sitting at 147 metres above sea level with unobstructed views in every direction, was well placed for the work. It could, in its active years, see the Inishturk Signal Tower in County Mayo some 15.5 kilometres to the north and the Bunowen Hill station roughly 17 kilometres to the south. Neither is visible from the site today: the Bunowen tower has been demolished, and the Inishturk ruin is too low to pick out at that distance. The whole network was abandoned by the mid-1810s once the threat of French invasion had receded. The Cleggan station's original layout can still be partially read on the ground: a small enclosure wall, now collapsed into a grassy bank with a rubble core, curves around the south and west sides of the tower, and a separate rectangular building stands in ruin about 40 metres to the west, already shown on the Ordnance Survey six-inch map surveyed in 1838 and 1839. A lime kiln was also marked on that same map immediately to the north-west of the tower, though its precise location is now buried under the rubble.

The site sits on a steep ridge above Cleggan Bay, surrounded by unenclosed blanket bog, with two small lakes visible to the east. About 765 metres to the north along the bay's coastline there is a court tomb, a type of Neolithic megalithic monument typically defined by a roofless ceremonial forecourt opening into a burial chamber, and roughly 945 metres to the south-east the first Ordnance Survey maps record a holy well named Tobernaseachtinnean. The signal tower occupies a landscape that was already old when the Board of Ordnance surveyors arrived, and the rubble that now surrounds it sits quietly among all of it.