Most Martello towers, the low, thick-walled coastal fortifications built across Ireland and Britain during the Napoleonic Wars as a defence against potential French invasion, read as simple cylinders. This one is subtly different: its eastern and western faces are flattened rather than fully curved, giving it a compressed, almost oval profile when viewed from certain angles. The exterior is faced in coursed limestone ashlar, and the whole structure measures around 14.2 metres in diameter, a substantial footprint for what was essentially a garrison outpost.

The tower is one of three that were positioned to guard the northern approach to Great Island, working together as a coordinated line of defence across what would have been strategically sensitive water. Inside, the layout follows the functional logic of its type. Four radially arranged rooms on the ground floor surround a central circular area, and the northernmost of these served as the magazine, sealed under a barrel vault of brick, a precaution that kept the powder store as isolated as possible from the rest of the structure. The first floor, now missing its floor surface, was lit by rounded-arch windows to the east and west, each flanked by fireplaces, an arrangement that made the flattened sides of the tower do double duty, providing both structural logic and liveable space for whatever small garrison was posted there. A brick dome covers the first floor level above, and the interior walls are lined throughout with brick. A spiral staircase on the south side of the entrance once connected ground level to the roof, though the steps are broken above the first floor and the upper section is no longer accessible.

The entrance, a rounded arch on the southwest face, sits at first floor level in the classic Martello manner, originally reached by a removable ladder that could be pulled up in the event of attack. A further opening to the north appears to be a later quarried addition rather than part of the original design. The bridge immediately to the north makes the tower easy to locate, though the interior is in a partial state of decay and the upper staircase should not be attempted.