H.M.Prison, Main Block (B.Wing)

H.M. Prison, Main Block (B Wing) is a building featuring robust Italianate detailing, constructed in a star plan layout. It has tall north and west wings with an octagonal center and a diagonally-placed entrance block, which is the larger part of the design. The building is four storeys high and constructed of coursed rubble with freestone dressings on the quoins and window surrounds. The roofs are made of corrugated asbestos, with oversailing eaves and massive square stacks topped with cappings.

The south-facing A wing has a total of 15 windows, with 8 on the lower level and 7 above, including three with lowered cills on the top floor to the left. The windows have iron grilles, and many retain their original cast iron frames. The B wing, which runs north, features similar detailing. The north and west gable ends have tall round-arched windows. The polygonal center has a brick infill wall on the east face, possibly intended for an unbuilt wing. The south wall's advanced center has an arched voussoir treatment, and a half flying-arch connects the north wing to the center.

The entrance block, which faces southwest, is two storeys high with a basement. It has rubble walls and a hipped roof, with an eaves cornice and a slightly advanced frontispiece featuring a round-arched bipartite window with keyblocks on the first floor. The entrance has a fine cavetto-moulded and rusticated doorpiece linked to a stringcourse, with a blind tympanum and lintel above modern double doors. A flight of steps leads south towards the gatehouse. Modern extensions flank the entrance block, connecting to buildings on both the left and right.

Inside, the interiors are primarily painted brickwork with open trussed roofs. Features include ironwork stairs, cantilevered landings with latticework handrails, and segmental arched heads to internal openings and doorways. There are also ironwork cell doors, metal grilles, and screens at the ends of the wings and corridors.