It's mid-Victorian, of course. The Victorians really the mastered Grim and Foreboding architectural school. It famously housed prisoners of war from the Crimean War. It held Irish rebels after the Easter Uprising, including Éamon de Valera.
Most famously of all (to my generation), Mick Jagger spent a night there in a drug bust. After which the editor of the Times wrote an editorial with the wonderful title, 'Who Breaks A Butterfly On A Wheel,' protesting the police decisions that had been made.
In 2003 there were riots in the prison protesting the conditions. They sound appalling, not the lovely 'Period Details' one might hope for in a mid-Victorian property.
The picture is captured from the internet, which I feel a bit guilty about. it was credited to David Hill/Daily Mirror.
The reason I used it is because this is the picture I took. It's pretty hilariously terrible.