Dunmahon Castle is a four-storey tower house built in the 15th century near Gibstown in County Louth, serving as a stronghold of the Plunket family until the late 17th century. The castle features a vaulted ground floor, north-eastern corner stairwell, and north-western garderobes, with an intact staircase still leading to the battlements. The castle is historically significant for a massacre during the 1640s involving Cromwell's troops that claimed an estimated 250–300 lives, and remains visible from both the M1 motorway and the Dublin-Belfast railway line.
