Blackrock Castle lies on the shore of the river Lee, in the city of Cork, in County Cork in Ireland.
The circular watchtower of Blackrock Castle was built in 1604, on the site of an earlier fort. With its 2.2 meter thick walls, it was designed to withstand cannon fire. It was built to defend the city against attacks from pirates and the Spanish, who had landed at Kinsale 3 years earlier. But it also served to protect the English Lord Deputy Mountjoy against the citizens of Cork, who had been slow to aknowledge King James I.
Later Blackrock Castle was used by the Mayors of Cork for the Admiralty Court. Also known as the Maritime Court, it exercised jurisdiction over all maritime caes and offences.
In 1827 the castle was gutted by fire following the annual Corporation banquet. Two years later, in 1829, it was rebuilt and enlarged in Gothic Revival style.
Later it was used as a meeting place, a private residence, a restaurant and commercial offices before it was acquired by the Cork City Council in 2001. At present the castle houses an astronomy center/museum especially aimed at children.