18 Castle Street, Duns

18 Castle Street in Duns is a former courthouse built in the later 18th century, now serving as a shop and house. The building is two stories high with an attic and features a three-bay façade. It has white painted harl with black painted ashlar margins.

On the southwest elevation facing Castle Street, there is a full-width base course and a blocked cavetto cornice. To the left, a deep-set panelled door leads to a flat, accompanied by a rectangular fanlight. To the right, the shopfront consists of a central two-leaf glazed panelled door with a rectangular fanlight, flanked by plate glass shop windows. The first floor has three regular windows, and the building has moulded eaves. There are also two gablehead dormers with brick infill.

The northwest side elevation has three bays, with windows on both floors to the left and a small window at the centre of the first floor. The broad irregular right bay features a panelled door at ground level and a small window to the right, with a large stair window above.

The northeast rear elevation is gabled and has two bays, with a window in each bay at both ground and first floors. At the centre of the gablehead, there is a round-headed window with a key-stone and impost-blocks, along with an apex stack.

The building has timber sash and case 12-pane windows, although the ground floor windows at the rear have been replaced. The stair window has multi-pane glazing. The roof is piended and gabled at the rear, covered with grey slates, and features ashlar coped skews with corniced skewputts.

Inside, the ground floor contains a courtroom at the rear, which has an egg and dart cornice. It features a screen of fluted Ionic columns with a bolection moulded frieze on the sides, along with a panelled judge's niche at the centre. Some fielded panelling remains behind later surfaces.