This is Portraine Martello Tower No. 7, one of a chain of coastal fortifications built along the Dublin coastline at a moment when a French invasion seemed not merely possible but imminent. The conservatory and chimney are later additions, quiet evidence of the long domestic afterlife that followed its brief career as a gun platform.

Construction of the Dublin-area Martello towers began in 1804 under the supervision of Colonel Benjamin Fisher of the Royal Engineers. Martello towers were squat, thick-walled round towers, originally developed as a form of coastal defence against naval attack, and the Irish examples were built in response to the threat posed by Napoleonic France. By December 1805, all the towers in the Dublin area were armed and complete. Twelve were constructed north of the city, each mounting a single 24-pounder cannon; the exception was the tower on Ireland's Eye, which carried two. No artillery batteries were built alongside the northern towers, Portraine included. After the Napoleonic Wars ended and the strategic justification evaporated, the tower passed through a series of hands: for a time it was occupied by an invalid Gunner, and by 1826 it had come under the ownership of the Coast Guard. The War Department retained it well into the twentieth century before it was eventually converted into a private residence.

The tower stands on the cliff edge to the east of Portraine, above the slipway. Approaching from the village, the conservatory addition at ground level immediately distinguishes it from its plainer counterparts along the coast. Look above the western entrance and you can make out the machicolation, an overhanging parapet with openings through which defenders could drop stones or other materials on anyone attempting to force the door, a feature that gives even a converted holiday home a faintly martial air. The tower is in private use, so the exterior and its clifftop setting are what a visitor can reasonably expect to see.