Ballincollig Castle is a Norman castle to the south of the town of Ballincollig, County Cork, Ireland built after the Norman invasion of Ireland. In its prime, the castle was inhabited by the Barretts, who had control of the local area. The castle still stands today, albeit heavily damaged. The original keep still remains, as does most of the curtain wall and two towers set therein.
There appear to be no early descriptions of the castle. Ballincollig Castle was constructed on a limestone summit, with a clear line of sight over the low land of the Maglin Valley. Beneath the castle there is a dark natural cavern which runs into the rock and around it the remains of a moat.
The castle consisted of a large walled enclosure (or bawn), with a tower or keep on one side of it and possibly a large hall through the middle. Most of the enclosing or outer wall remains. It is about 5 feet (1.5 m) thick and 15 feet (5 m) high. The space on top was defended by a parapet with flights of steps leading up at several points. There were two defensive towers on the wall, one at present in ruins in the south-east corner and the second on the south wall.
The enclosure is between 70 and 100 feet (21 and 30 m) across and is rocky and uneven. There appears to be evidence of a hall in the middle as one portion of the outer wall has the remains of a fireplace and chimney and a window of two lights. It is suggested that the towers on the outer wall and the hall are of 15th century making and were probably built after the sale of the castle to the Barretts.
On the other hand, the main tower or keep is of the 13th century and was used by Coll. The keep was repaired by the Wyse family in 1857 and on the east wall a shield has been inserted bearing the monogram W with the date 1857 beneath it. The keep is 45 to 50 feet (14 to 15 m) high. The ground floor is vaulted and originally had no entrance to it except by a trap door from above, so it was probably a prison. The room on the first floor had a path up to it, carried on arches. It is about 7.5 by 9 feet (2.3 by 2.7 m). A very narrow staircase leads to other stories, all of which have stone floors on solid arches. To support them the two walls on which they rest are thicker than the others. The second story has seats in the lambs of the loopholes, a drain from a lavatory and a small square cupboard in the wall over it. The upper floor of chief chamber seems to have had windows added on all sides in the middle of the 19th century. However, there are loopholes in other parts of the walls of the keep. The lack of windows and a fireplace and the fact that the small rooms occupied all the internal space between the walls suggests that the building was more of a keep for last defence than a regular living quarters.