Three storeys tall, roofless, and circular in plan, it has an internal diameter of just 3.65 metres and walls a full 1.2 metres thick, built from granite and finished with a corbelled parapet, the kind where projecting stones support the upper edge without the need for conventional brackets. Whatever lantern or fire once occupied the top is long gone, open now to the sky above Gleann Oirtheach.

The structure sits to the south-west of a signal tower, the two linked by a passageway, and the arrangement tells you something about how this stretch of coastline was once watched and managed. Signal towers, a network of which was constructed along the Irish coast during the Napoleonic Wars in the early nineteenth century, were built to relay warnings of enemy vessels by line of sight from one tower to the next. A lighthouse alongside such a tower, with attached dwellings and out-offices, suggests a small working compound, self-contained and permanently staffed, positioned to serve both the warning network and the navigation needs of passing ships. The high enclosing wall would have offered some shelter from the Atlantic weather that defines life on the southern Irish coast.