Mentioned by Lonely Planet Top Choices
Top things to do in Ireland
"This low-lying green island in Cork Harbour was once an important part of the port's defences, topped by an 18th-century artillery fort. In the second half of the 19th century, during the Irish War of Independence, and from 1984 to 2004 it served as a prison, gaining the nickname 'Ireland's Alcatraz'. Today you can enjoy a guided walking tour of the former prison buildings, then go off and explore on your own; the ferry departs from Kennedy Pier, Cobh."