That combination, a medieval fortress that was besieged during the Cromwellian wars of the mid-seventeenth century and yet retains a lived-in wing, gives Ardfinnan Castle a quality somewhere between monument and home, with the visual evidence of both periods visible in the same structure.

The original castle here dates to the thirteenth century and was built to command the river crossing and the settlement below, a position that made it strategically important for several centuries. The later tower house, measuring roughly six metres by ten metres externally, was constructed onto the south-east angle of what would have been the bawn, the walled enclosure that formed the defensive yard of the earlier castle. A bawn was a standard feature of medieval Irish strongholds, providing a protected outer space for livestock and garrisoning. Despite surviving to a height of at least four storeys and being rendered in plaster, the tower has lost almost all of its original windows; only a single loop in the east face may be original. What does survive architecturally includes a series of crude dripstones, the projecting mouldings set into the uppermost masonry courses to throw rainwater clear of the wall face, and a pronounced base-batter, the deliberate outward splaying of the wall at ground level that added both structural stability and defensive resistance. A caphouse, a small roofed structure running north to south along the east wall, is also visible. The castle endured a siege during the Cromwellian campaigns of the 1640s and 1650s, a period of widespread destruction across Irish fortifications, though the structure evidently survived in sufficient condition to remain habitable in some form.