Drumharsna Castle, Medieval tower house in Ardrahan, County Galway, Ireland

Drumharsna Castle is a stone tower house near Ardrahan, County Galway, known in Irish as Caisleán Dhroimm Tharsna. It is a national monument of Ireland. The sources record no details of its walls, windows, chimneys or interior, so its appearance should not be described beyond its identity as a tower house.

Drumharsna Castle was owned by Shane Ballagh in 1577 and was probably built some time before that. In 1920 it was occupied and damaged by the Auxiliary Division of the Royal Irish Constabulary, D company from Galway stationed at Lenaboy house. Two brothers, Patrick and Harry Loughnane, arrested on 26 November 1920, were taken there and tortured and murdered; their mutilated, burnt bodies were found in a nearby pond over a week later.

The castle's Irish name, Caisleán Dhroimm Tharsna, refers to the ridge it stands on. In 1920 it was occupied by the Auxiliary Division of the Royal Irish Constabulary, and it was here that brothers Patrick and Harry Loughnane were taken after their arrest on 26 November 1920; their bodies were found in a nearby pond over a week later.

Drumharsna Castle stands in open farmland near Ardrahan, County Galway, reached by minor roads; there is no visitor centre, car park or guided tour. The tower house is a national monument, so view it from the surrounding ground and do not enter the structure. The field setting is exposed to wind and rain, and the ground around the walls is uneven.

The castle is linked to the Loughnane brothers: Patrick, an IRA officer in the Beagh Company, and Harry, secretary of the local Sinn Féin cumann, were arrested by Auxiliaries on 26 November 1920 and taken here. Their mutilated, burnt bodies were found in a nearby pond over a week later.