The Punishment Block is the only purpose built cell block in the Fort. It was built in response to the murder of Warder William Reddy in 1856.
Work began in 1858 using local limestone with military and convict labour and it was opened in 1860.
It consisted of twenty eight solitary confinement cells and housed the ‘Penal Class’, considered the most dangerous prisoners. They were heavily chained and clothed in black from head to toe, with a veil hiding all but their eyes.
Conditions inside the block were the harshest inside the prison. At first the cells were furnished with only a stool and convicts slept on the floor. Prisoner descriptions of medieval conditions in a Victorian prison outraged many. There were several suicide attempts and the block was the main reason that Spike Island was described as "Hell on earth" by the penal classes.
During the convict era 1847-1883, it housed political prisoners.
For several years it was referred to as the Mitchel Block as it was incorrectly believed that he was held there in 1848.
Today visitors can see the Guard room and learn how archaeologists worked on the site. The Dark Cells can be explored by torchlight while modern solitary cells are also on view. The cells of Patrick Tierney and John Mitchel are both interpreted and the upstairs rooms of the block contain an art exhibition of prisoners pieces from the modern era.