This grassy mound, measuring 22 metres north to south and 34 metres east to west, rises about three quarters of a metre above the surrounding landscape. Today, only gentle undulations in the turf hint at the castle's former presence; the stone that once formed its walls met a rather practical fate in 1826 when it was ferried across to Skibbereen and repurposed to build the town's Pro Cathedral.

The castle belonged to the O'Driscoll clan, one of the most powerful maritime families in medieval Cork. From this strategic position, they could control shipping traffic through the estuary whilst maintaining a watchful eye over their coastal territory. The O'Driscolls were renowned for their naval prowess and their network of castles along the southwest coast, of which Donegall was an important link in their defensive chain.

Archaeological surveys have recorded the site's dimensions and confirmed its historical significance, though visitors today will need a good imagination to picture the fortress that once stood here. The transformation of a clan stronghold into the foundations of a cathedral serves as a rather fitting metaphor for the changing power structures in 19th century Ireland, when ecclesiastical authority was replacing the old Gaelic order that had dominated these lands for centuries.