In 1582 a fortification was built on this site, and later around 1600, a round tower was constructed to safeguard against pirates "carrying away" vessels entering the harbour.
This circular tower on the water's edge, is the earliest element of this structure to remain today
In 1722 the old four-storey tower was destroyed by fire and new one built by the citizens, costing £296.
Following a banquet, the castle was destroyed by fire in 1827. The rebuilding was completed in March 1829 and cost the City of Cork £1,000. The neo-gothic complex of buildings around a courtyard, designed by George and James Pain aka Payne is essentially what remains today.
The castle entered private hands and was a private residence for a time in the 20th century. In 2001 the building was reacquired by Cork Corporation who commenced on renovating and re-purposing the complex as an observatory and museum.