20 Charlotte Square, Edinburgh

18 Charlotte Square in Edinburgh is a neoclassical palace block designed by Robert Adam in 1791, with most of the construction completed between 1803 and 1807, and early 20th-century attics added later. This symmetrical building features three stories, a basement, and an attic, originally consisting of six individual houses. It is part of a pair flanking the former St George's church, now known as West Register House. The exterior is made of polished cream sandstone ashlar, with a rock-faced basement and V-jointed rustication at the ground floor, complemented by an impost course where necessary, and cill courses on the first and second floors. The building is topped with a cornice and blocking course.

The east elevation facing Charlotte Square has a slightly projecting five-bay centerpiece with a tetrastyle porch at its center, which contains a pair of doors topped by a large tripartite window with Ionic columns and a massive glazed fanlight. The outer bays are flanked by Ionic columns with balustrades between the column bases, and there is a fluted frieze with a blank panel at the center. The end pavilions feature giant pilasters on the upper floors, arched tripartite doorways in the inner bays, and a tripartite window in a round-arched recess on the first floor. The southern pavilion has a pyramidal roof, while the northern pavilion includes a full pilastered attic storey. The inner three bays are arcaded at the ground level, with rectangular windows and arched tripartite doorways. Nos 19 and 22 have pairs of canted piend-roofed dormers, and No 21 has a bipartite dormer.

To the north, there is a five-bay coursed rubble gable with some blind windows, which is extended by a single-storey, five-bay range from the early 20th century on a rusticated basement, featuring a pilastered two-storey end pavilion. The building is immediately adjacent to Hope Street to the south. The rear has a full attic storey.

The windows are timber sash and case, with 12 panes, while the centerpiece, northern pavilion, and No 22 on the first floor have 15 panes. The building has corniced ashlar stacks and is roofed with grey slates.

Inside, No 18 features an enriched ceiling in the former drawing room, and No 23 has fine enrichments from around 1905, with possibly earlier details. The rest of the interior was unseen as of 1995.

The property is also accompanied by cast-iron spearhead railings, original lamp standards, and rubble boundary walls at the rear.