Armoury at Fort Williamsburg including attached screen walls

The Armoury at Fort Williamsburg is a roughly square building dating from the 19th century. It features a Neo-classical design on the north-west side facing the parade ground, while the rear has some simple Gothick elements. The building is mostly single storey, but it has a two-storey section at the rear. It is constructed of rubble, primarily cement-rendered, and has a slate roof with wide eaves and paired, dentilled brick chimney stacks.

The main front has three bays and is highlighted by a pediment created by a toothed cornice above three tall round-arched openings. The central opening, originally a doorway, has been converted into a window. The windows are small-pane three-tier sashes, including lunettes. An impost band and corresponding bases give the appearance of pilasters. There are 9-pane sashes on the sides. The rear, which faces the Barracks, is also made of rubble and has blocked first-floor openings, with only one small-pane pivot window remaining. At either end of the ground floor, there are boarded doors with pointed-arched heads set within square-headed openings. Between these doors are three 2-light windows featuring Gothick small-pane casement glazing, supported by slate lintels.

Attached to either side of the building are quadrant screen walls made of rubble, each with arched gateways leading into the former parade ground. The southern wall returns to a tunnelled gateway that leads into the barracks.

The fort itself is roughly square in shape, with redans at each of the four corners, surrounded by ditches and revetment walls. The building was not accessible at the time of inspection as it was being used for storage by Gwynedd Archives.