This modest structure, marked as ruins on the 1842 Ordnance Survey map, consists of a low, grass-covered square area measuring roughly 6.3 metres northeast to southwest and 4.4 metres northwest to southeast. The antiquarian Thomas Johnson Westropp, writing in 1915, described it as a turret, though its exact original function remains somewhat unclear.

The castle ruins occupy a strategic position on the inner bank of the fort, right at the cliff’s edge, offering commanding views across the harbour to Dunmanus castle on the southern shore. This placement suggests it served as part of the defensive network controlling access to this important waterway in West Cork. The O’Mahoney clan, who gave their name to the structure, were prominent landowners in the region during the medieval period and built several fortifications throughout the area.

Today, visitors to Knockeens will find little more than the grass-covered foundations of this once-important stronghold. The site was officially documented in the Archaeological Inventory of County Cork, Volume 1, published in 1992, with updates added as recently as 2009. While the physical remains may be modest, the location offers a tangible connection to the complex web of alliances and rivalries that shaped this corner of Ireland during the centuries when tower houses and fortified dwellings dotted the landscape.