Bardsey Island Lighthouse with attached keepers' house

Bardsey Island Lighthouse, along with its attached keepers' house, is a notable structure. The lighthouse tower stands 30 meters tall and has a square shape that narrows as it rises, which is an unusual design for a Trinity House building from its period. The tower is constructed of limestone ashlar, with its exterior finished in red and white bands. Access to the lighthouse is through a lobby that connects it to the attached stores and the keepers' accommodation. The upper floors feature small mullioned casement windows, and there is a moulded cornice at the lantern walkway, which is surrounded by bellied cast iron railings. The lantern itself is canted and octagonal, with both horizontal and inclined vertical glazing bars, a metal roof, and a top railed balcony that was added after 1886.

The keepers' house is connected to the tower at the west end by a single-storey corridor that has a central doorway and sidelights. This accommodation building is also single-storey with attics and features a four-window, double-pile range. It is rendered over rubble, whitewashed, and topped with a slate roof that has overhanging eaves and two axial stacks. The roof is gabled at the east and half-hipped at the west. The east gable end has a two-window range and a gabled porch to the left with overhanging eaves. The original windows appear to be 12-pane sashes, with three single windows on the south side and a pair to the right of the center, although some of these windows are blocked. There are also two dormer windows in the roof, which are 12-pane sashes.

Inside the tower, there is a general store at the base with a shallow vaulted slab ceiling, and a similar room on the first floor. The stairs, which are cantilevered from the tower walls, feature moulded stone risers and plain cast-iron rails. A cast-iron tube for the weights of the clock-work rotative mechanism for the lantern is braced to the external walls at the second floor level, and there is a service room located below the lantern. The optic, installed in 1883, is a first order catadioptric lens with five equal panels that revolves on a bed of mercury. This lens is supported by a cast-iron base, with cylindrical shafts that have moulded capitals and brackets.