The main L-shaped block for men at the centre of the prison compound and directly north of the gatehouse.This block dates from 1861 when the entire prison was rebuilt and enlarged (at a cost of over £30,000), with some later additions.

There is robust Italianate detailing to entrance block, and tall north and west wings, forming an octagonal centre with the diagonally-placed entrance block (forming the larger part of the star plan). the block is four storeys, cinstructed of coursed rubble with freestone dressings to the quoins and window surrounds. It has a corrugated asbestos roofs, with oversailing eaves and massive square stacks with cappings. B wing has 15 windows facing south to A wing, with three lowered cills to the top floor, and iron grilles to the openings, many with original cast iron window frames behind. There is similar detailing to B wing running north, and tall round arched windows to the north and west gable ends.

There is a polygonal centre with a brick infill wall on east face (possibly for an unbuilt wing?), arched voussoir treatment to the advanced centre of the south wall, and half flying-arch attaches to the centre of the north wing.

Ther is a two storey and basement entrance block facing the south-west, constructed of rubble walls, with a hipped roof, eaves cornice, and a slightly advanced frontispiece with a round-arched bipartite window with keyblocks to first floor. The rusticated doorpiece has fine cavetto-moulding and a keyblock linked to the stringcourse, a blind tympanum and lintel over modern double doors, and a flight of steps orientated south towards the gatehouse. Modern extensions flank the entrance block with links forward to the buildings on the left and right.

Interiors are mostly of painted brickwork, with open trussed roofs, ironwork stairs, cantilevered landings with latticework handrails, and segmental arched heads to the internal openings and doorways. There are ironwork-cell doors, metal grilles and screens to ends of wings and corridors etc.
(source; Cadw listing database) S Fielding RCAHMW 20/10/2005