Old Lower Lighthouse, with boundary walls and coastguard house

The Old Lower Lighthouse, built in 1869 and modified in 1960, is located on Portland Bill Road in Portland. This lighthouse features a slender, tapered cylindrical tower topped with a lantern, and is accompanied by a domestic block to the northeast, which is connected by a flat-roofed, one-storey annular extension from around 1960. The exterior is rendered and painted, with slate roofs.

The tower includes various openings, with two-light casements set in deep reveals beneath cambered projecting lintels and plain cills. It is crowned by a bold cornice that supports a cast-iron balustrade featuring heavy posts and three plain rails around the lantern balcony. The single-storey extension has 20th-century steel casements. The domestic block is two storeys high, featuring an original three-window unit and a slightly smaller, lower unit added to the left. It has twelve-pane sash windows, a central gabled porch, coped verges with bold kneelers, and a prominently modeled linked triple stack on the left gable, with a double stack on the ridge to the right of the entrance. The extension also has a gable stack on the left.

The first lighthouse on this site was built in 1716, replaced in 1789, and again in 1869. It was decommissioned in 1906 when the New Lighthouse opened, at which time the commemorative plaque from 1789 was moved to the New Lighthouse. Since 1962, the Old Lower Lighthouse has been used as a bird observatory, functioning alongside the Old Higher Lighthouse.

The property is enclosed by a rubble boundary wall topped with half-round oversailing copings and features a set-back quadrant at the entry on the north side, marked by a pair of square piers with pyramidal cappings.