Dunmanus Castle is the largest and best preserved, of the many O'Mahony castles on the Mizen Peninsula. Because they traded with Europe most of their castles in the West Cork were built near the sea. This fine castle is situated on the southern side of Dunmanus Bay on a turtle- shaped rock, in a very romantic and picturesque site.
According to archaeologists, it is likely that the castle was constructed in 1430 A.D. by Donogh More O'Mahony. I has six flanking towers connected with walls. It has a dungeon below the ground floor, unique in O'Mahony castles. There are three floors, each with vaulted ceilings and the corner tower, another unusual feature with five floors. There is a rather complicated series of interior stairways because of this.