The plan of the prison comprised a circular chapel at the centre of the site, surrounded by a three-storey hexagon made up of the governor's quarters, administrative offices and laundries, surrounded in turn by six pentagons of cell blocks. The buildings of each pentagon were set around a cluster of five small courtyards (with a watchtower at the centre) used as airing-yards, and in which prisoners undertook labour. The three outer angles of each pentagon were distinguished by tall circular towers, described in 1862 as "Martello-like": these served in part as watchtowers, but their primary purpose was to contain staircases and water-closets. The third and fourth pentagons (those to the north-west, furthest from the entrance) were used to house female prisoners, and the remaining four for male prisoners.