Dunasead Castle, Medieval castle in Baltimore, Ireland.

Dunasead Castle is a two-storey rectangular fortified house with an attic, about 6 by 18 metres, set into the south-west wall of a bawn or curtain wall on a sandstone ridge above Baltimore harbour. Its ground-floor windows are narrow slits and a bartizan stands on the south-west corner. It was probably built in the 1620s and is now a private residence.

The original structure was built in 1215 by Anglo-Norman settler FitzStephens and suffered destruction in 1305 when the MacCarthys attacked it. Afterward, the O'Driscoll clan took control and made it a significant stronghold for their coastal operations.

The Irish name Dún na Séad means "fort of the jewels". The castle is traditionally associated with the O'Driscolls, the Gaelic sept that held it after the MacCarthys burned the earlier tower in 1305. A feud with the merchants of Waterford, begun in 1368, ended with a Waterford fleet sacking Dunasead in 1537.

Dunasead is a private residence, so there is no general admission and the interior is not open to visitors. It stands on a sandstone ridge in the centre of Baltimore, a short walk from the harbour, and its bawn wall and exterior can be seen from the street. Restoration ran from 1997 to 2005, and the castle was partially opened to the public from 2005.

The castle's defensive features are modest for a tower house: ground-floor windows are narrow slits, and a bartizan projects from the south-west corner. The main block, set into the south-west bawn wall, measures about 6 by 18 metres. The bawn or curtain wall still encloses the building on its sandstone ridge above the harbour.