At Lusk, a five-storey square medieval tower rises from a natural prominence within an old ecclesiastical enclosure, and its north-east corner is not a purpose-built turret at all but a much earlier round tower, the kind of tall, tapered stone structure associated with early Irish monasteries, incorporated bodily into the later medieval fabric. The other three corners have their own projecting turrets with stepped battlements, giving the whole structure a compact, slightly asymmetrical bulk that rewards a second look.

The tower is all that survives of what was once a substantial parish church, roughly fifty metres long and divided into two aisles by a seven-arched arcade. That building was demolished in the nineteenth century, leaving only the western tower standing, as recorded by Harold Leask. A replacement church was constructed in 1847 and effectively grafted onto the tower's western face, which is now the entry point for anyone wishing to explore the older fabric. Inside, the ground floor retains a barrel vault, a continuous arched stone ceiling, with visible traces of wicker-centring, the imprints left by the woven timber framework used to support the vault while the mortar set. The upper floors are reached by a stairwell in the south-east turret, and the doorways throughout are finished with a double-centred pointed arch and late medieval hammer-dressing, a technique that leaves a characteristic tooled texture on the stone. The contents gathered within the tower are, if anything, stranger than the architecture: a bullaun stone, a heavy boulder with a carved hollow basin associated with early Christian sites; a seventeenth-century font; and a decorated fireplace surround removed from Bremore Castle, carved in false relief with six heraldic shields framing a scene of the Annunciation. Two grave slabs commemorate Walter Dermot, who died in 1538, and James Birmingham, who died in 1637, the latter showing a relief effigy of an armoured knight alongside the arms of the Birmingham and Fitzwilliam families. On the first floor, a Renaissance table tomb carries high-relief effigies of a knight and a lady, erected in the mid-1580s in memory of Sir Christopher Barnewall, who died in 1575, and Marion Sharl.

Lusk is a small town on the main road north from Dublin towards Skerries, and the tower sits centrally in the village, visible from the road. The 1847 church is the access point; visiting hours depend on local arrangements, so it is worth checking in advance rather than assuming the tower interior will be open on arrival. The belfry stage at the fourth floor has double-light windows on all sides and access to the parapet, which gives a clear view over the flat north Dublin landscape and makes the unusual composite structure, medieval tower fused with early medieval round tower, easier to read from above than from the ground.