Carrickmines Castle, Medieval defensive castle in Carrickmines, Ireland.

Carrickmines Castle is a medieval fortress in County Dublin with towers, curtain walls, and a keep carved into the bedrock. The remains are now built into the M50 motorway roundabouts and are not accessible to visitors for safety reasons.

Built in medieval times, the castle was home to the Walsh family. It was besieged by English forces in 1642 during the Irish Rebellion, resulting in heavy casualties among defenders.

The ruins sit beneath and beside the M50 motorway roundabouts, making it an unusual archaeological location today. Excavations uncovered thousands of objects including weapons, coins, and pottery from medieval times.

The ruins lie within and beneath the M50 junction and its roundabouts, so there is no public access to the site itself. The motorway area is not a place to walk; the surviving walls and defences can only be seen from passing roads. The junction and motorway were completed in 2005.

The "Carrickminders" camped on the ruins in 2002, not the 1980s, to stop their removal for the M50. Among them were Vincent Salafia and Gordon Lucas, joined by TCD historian Seán Duffy and site director Mark Clinton. They questioned why the route was moved through the castle in 1998 after being routed around it in 1983.