Castle Donovan (Irish: Caisleán Uí Dhonnabháin) or Castledonovan or O'Donovan's Castle refer to the remains of an Irish tower house or túrtheach, in a valley near Drimoleague, of medium size which was the so-called "seat" of the Clann Cathail sept of the O'Donovans for a period during the 16th century.

Approximately 60 feet in height, it sits on a large rock or outcropping, which forms the ground floor, close to the bank of the River Ilen.

It is believed that his father had already relocated the family in the first decade of that century to the more profitable Rahine Manor on the seacoast to protect their maritime interests.

[2] According to tradition the tower was severely damaged by Oliver Cromwell's soldiers in the late 1640s, blown up with powder in retaliation for Donal III O'Donovan joining the Stuart side and for his involvement in the rebellion and massacres of 1641, and has been uninhabited since that time.

[citation needed] In 1834, J. F. W. writing for editor Philip Dixon Hardy published an account of his 1828 journey to the "vale of Castle Donovan", including a drawing in which several of the outbuildings can still be seen, in the Dublin Penny Journal.