Aghamarta Castle, lies in a field, east of the town of Carrigaline, in County Cork in Ireland.
Aghamarta Castle was probably built in the 12th century. In the late 17th century the castle was sold by the Earl of Shannon to the Pomeroy family.
In 1824 Aghamarta Castle was bought by the O'Grady family. Then the castle was in great disrepair, and the O'Grady's used stone from the castle in the construction of the present mansion in 1830. The O'Grady's sold the property in 1916.
At present the mansion is used as a school and the ruin of Aghamarta Castle lies in the grounds of this school. These grounds are used as a school garden. It is a small but nice ruin.