It is the largest of the Martello towers built around the harbour, yet it sits largely sealed off: the iron door at first-floor level on the east side is shut, and whoever last tried to make something useful of the building left only enlarged window openings on the north, south, and west faces as evidence of their intentions. Those widened opes suggest a conversion that never quite happened, lending the structure an unfinished quality that is oddly more interesting than if it had been neatly repurposed.

Martello towers were a British coastal defence measure, squat circular forts designed to resist artillery and to mount guns at their parapets. The name derives from a tower at Mortella Point in Corsica, which proved stubbornly difficult to capture in 1794 and inspired widespread imitation along vulnerable coastlines. The Ringaskiddy example was under construction between 1813 and 1815, a period when the threat of Napoleonic invasion, though fading, had not entirely dissolved. It is built of coursed limestone ashlar and sits within a circular enclosure roughly a hundred metres across, the boundary marked by ordnance stones. Around it runs a dry fosse, a wide defensive ditch cut into the ground rather than filled with water, measuring about four and a half metres across and three metres deep. The tower itself is not quite symmetrical: its profile is notably flattened to the north and south, giving it slightly irregular dimensions of around fifteen and a half metres east to west and under eleven metres north to south, with a height of just over twelve metres.

The site is on the Ringaskiddy promontory, an area now dominated by pharmaceutical industry and port infrastructure, which makes an encounter with the tower feel genuinely incongruous. It is not accessible internally, and the surrounding enclosure means the best impression of its scale comes from approaching across the high ground where it commands its original field of view across the water.