21, Castle Street

21 Castle Street is a late 18th-century house that has been used for commercial purposes and is currently unoccupied. It features Flemish bond brickwork with light headers, set on a chamfered plinth, with all dressings made of calciferous sandstone, some of which are painted. The building has V-jointed quoins and a dentilled cornice, topped with a graduated greenslate roof and 18th-century end brick chimney stacks. The house is two storeys tall, with five symmetrical bays and rear extensions that create an overall L-shape. It has a double-depth, central-stair plan.

The central entrance features a panelled door with a radial fanlight, accessed by steps and set within an open-pedimented doorcase that has a block entablature, panelled reveals, and soffit. The sash windows, which have glazing bars (except for the lower panes on the ground floor), are framed by stone architraves. The linear rear extensions consist of three builds and include sash windows and a tripartite window, along with a canted bay window at the rear of the house.

Inside, the property retains many original 18th-century features, including panelled doors in fluted architraves with panelled reveals, moulded plaster ceiling cornices, and panelled bands. There are several black marble fireplaces, as well as one carved wooden fireplace adorned with swags, roundels, and a fretted mantel shelf. The wooden staircase features carved tread ends, delicate scrolled wrought-iron balusters, and a moulded wooden handrail, leading to an arched hall and landing.