Built in the 16th century, this castle, also known as Castle Carrick, occupied a strategic position on a low rocky plateau overlooking the water. The O'Reillys reoccupied their fortress in the 17th century, but according to local tradition, Oliver Cromwell's forces ultimately brought about its destruction during his brutal campaign through Ireland in the 1650s.

The castle's design reveals the defensive priorities of its builders. At its heart stood a keep, raised on a mound about 1.8 metres high, surrounded by a roughly rectangular bawn measuring 53 by 32 metres. The landward approach faced two projecting towers at the southeast and southwest corners, whilst rock-cut fosses provided additional protection; the eastern fosse stretched about 4.2 metres wide, the western 5.1 metres, with a narrower, shallower defensive ditch on the southern side where the entrance likely stood. The bawn walls rose approximately 1.6 metres above these fosses and the river level, creating a formidable barrier against attackers.

Today, nothing remains visible at ground level of this once-imposing fortress. Archaeological surveys conducted in 1942 and later studies by Davies in 1947 and Wilsdon in 2010 have pieced together the castle's layout from subtle traces in the landscape. The site now exists only in historical records and local memory, a ghost of the O'Reilly power that once commanded this stretch of the Annalee River.