A thousand years ago the O’Mahonys were a powerful sept occupying a swathe of territory running from where now stands Cork city to the south-west of the region. However, following the Norman invasion in the second half of the 12th century the O’Mahonys were gradually pushed ever closer to the region’s Atlantic extremities, ultimately settling on the peninsulas that jut into the ocean. Here, according to the medieval Annals of Inisfallen, they built themselves a fortified settlement in a place now known as Dunlough Castle. It is easy to understand why the location was chosen. To the east lies a lake, Dun Lough which would have provided fish for the building’s occupants. To north and south the land rises making it possible to anticipate any potential attack, since those responsible would have been visible on the horizon. Meanwhile immediately to the west are cliffs dropping precipitately to the Atlantic. As Peter Somerville-Large, who formerly lived in this area, wrote more than thirty years ago: ‘To an invading army, the cliff edge, the defensive wall, the lake and the sternly inaccessible approach would have made the castle appear impregnable.’

In this sheltered spot Donagh na Aimrice O’Mahoney (Donagh the Migratory) erected a castle on what is believed to have been the site of an Iron Age fort. What we see here today, however, are the remains of a 15th century development. This gives Dunlough its popular alternative name of Three Castles since the structure comprises three fortified towers joined by a wall some twenty feet high and almost 1,000 feet long running from cliff face to lakeshore. All three towers are rectangular and of three storeys, the most substantial being that furthest to the west. Rising almost fifty feet and over fifty square feet inside, the building would have served as residence for the owners. It has entrances on both the ground and first floors, the latter presumably accessed by means of a ladder, to provide additional protection for occupants in the event of an attack. Internally the first floor was of wood and is therefore long gone but the second floor, of stone, survives: the space above would have been used for dining and large gatherings. The roof of towers from this period was typically of wood and so no longer extant.

The middle tower at Dunlough was probably used for storage and that closest to the lake provided ingress to the whole site. The construction technique used throughout was dry stone masonry, unusual for the period when wet mortar and sand were used in building; dry stone masonry had been common at an earlier date meaning Dunlough was somewhat anachronistic, the reason perhaps being its remote location. The stone used – indigenous schist-slate rock – was quarried from local pits. The nature of its construction left the building vulnerable to decay, since it appears Dunlough was never subject to serious attack. The O’Mahonys remained there until the 1620s when their lands were confiscated: the last occupants are believed to have been members of the O’Donohue family, all of whom apparently died by murder or suicide: according to legend a drop of blood falls every day in the tower closest to the lake. Whether true or not – the building today looks clear of all bloodstains – the story adds to Dunlough’s inherently romantic character.