This is one of a line of castles (including Kilbolane castle) built in the 13th century to defend Norman territory to the east against attack from the west by resurgent Gaelic clans. This type of castle has no central keep (tower) but relies for its defence on substantial curtain walls, roughly seven-metre high and two-metre thick, linking circular towers at each corner.
The external base of the wall is sloped outwards (battered) for extra strength, and the castle was surrounded by a deep moat for added defence. The top of the walls had battlements with a wall walk along the inside to allow soldiers to keep a watchful eye on the surrounding countryside. The openings in the walls were tall narrow slit arrow-loops, designed to allow the defenders of the castle to shoot outwards but also protect them from hostile fire. The southeast corner tower, to your left, contained a well (now covered over) which was an essential part of a castle.
The main entrance into the castle is the barrel-vaulted passage in the square tower midway along the south curtain wall. The entrance was the weakest point in a castle's defences (being the largest opening through the walls) and therefore needed extra protection. This included a substantial outer door and portcullis; the vertical recess that housed the sliding portcullis is evident on the sides of the passage. The entrance tower was substantially enlarged and rebuilt in the 15th century, as evidenced by the ogee-headed windows.
Liscarroll was long associated with the Norman family of de Barry, in whose North Cork territory it lay. The castle was claimed by Sir Philip Perceval, who had mortgaged it from the de Barrys, in the early 17th century. It featured in the wars of the 1640s and in 1650 it was attacked with artillery by Parliamentary forces and a breach was made in the western wall. After the Cromwellian settlement, ownership of the castle returned to the Percivals and remained in their hands until recently.