Castle Donovan, 16th-century tower house in County Cork, Ireland

Castle Donovan is a roofless tower house of rough grey and brown stone on a grassy slope above the River Ilen near Drimoleague. It rises about 60 feet from a rock outcropping that forms its ground floor. The upper walls are broken and uneven, and the surviving western wall collapsed except for the spiral staircase. Scaffolding in green netting covers part of one side, and a fence marked "DANGER KEEP OUT" surrounds the base.

The tower was originally called Sowagh while the O'Donovans lived there before the 17th century. It was built or enlarged by Donal of the Hides, Lord of Clancahill, from about 1560 until his death in 1584. His son Donal II O'Donovan repaired or altered it decades later, but the family had already moved to Rahine Manor. The name Castle Donovan comes from a regrant by James II in 1615.

The tower's original name was Sowagh (also Sooagh or Suagh) while the O'Donovans lived there before the 17th century; the name Castle Donovan comes from the Manor of the Castle of O'Donovan and a regrant by James II of England in 1615. It was the seat of the Clann Cathail sept of the O'Donovans for a period in the 16th century.

The tower stands roofless on a grassy slope near the River Ilen, with a low metal fence and a "DANGER KEEP OUT" sign at its base; scaffolding in green netting covers part of the left side. The Office of Public Works carried out conservation between 2001 and 2014, but the masonry was cracked by a 17th-century explosion and the western wall collapsed, so the structure is not safe to enter. View it from the fence line.

The 1640s powder blast left only a small gouge in the southwest corner, but the shock cracked the masonry so badly that the whole western wall, apart from the spiral staircase, and most of the southern wall later collapsed. The Office of Public Works conserved the tower between 2001 and 2014.