This remarkably well-preserved round tower stands on a low hill just 12 meters southwest of St. Caimin’s church on Inis Cealtra (Holy Island) in Lough Derg. Unlike many Irish round towers that taper to a point, this one has a distinctive flat top.

The tower showcases exceptional medieval craftsmanship, with carefully laid stone courses and unusually large blocks forming the foundation. The base measures 4.58 meters across, narrowing slightly to 4.5 meters at the doorway level. About 30 centimeters above ground, the wall steps inward by 10 centimeters—a feature that excavations in 1976 revealed extends 40 centimeters deep into the ground, sitting on a thin layer of small stones and natural rock.

Inside, the tower has been excavated down to 60 centimeters above this external offset, revealing large stones projecting from the interior walls that correspond to the massive external blocks. The builders created multiple floor levels using a combination of rough stone offsets and carefully placed corbels (stone brackets) topped with flagstones. The first floor sits 2 meters above ground level, with three additional floors marked by offsets higher up.

The entrance, positioned on the east-northeast side, features a round-headed doorway measuring 64 centimeters wide at the base and 1.6 meters high. Both the lintel and sill are single, massive stone slabs that run completely through the thick walls. Above the second floor, a large, finely dressed window with an angled head faces north, while three square-headed windows face east-northeast, south-southwest, and northwest at ascending levels.

Archaeological excavations revealed the careful planning that went into the tower’s construction. The builders first laid down a large oval foundation of puddled clay reinforced with small boulders and stones, surrounded by drainage trenches. Evidence of a wooden stairway was found on the northwest side—a series of post-holes that archaeologists believe supported steps leading up to the elevated doorway.

The excavations also uncovered several burials between the round tower and St. Caimin’s church, highlighting the site’s long history as a place of worship and burial.