Disobedient son's punishment gives O’Donoghue’s Prison Island its name

O'Donoghue's Prison Island, County Kerry: chieftan O'Donoghue used this little island to punish his son for some act of disorder or disobedience
Its formidable cliff walls of limestone forbid any entry to this islet in the Lakes of Killarney. And that fortress-like appearance made it a perfect choice for exactly that purpose.
This is no island at which to linger such as the soul-soothing Innisfallen just a bit further out from Ross Castle. This is a place to imprison your foes.