21 Marine Place, Rothesay, Bute

20 Marine Place is a near-symmetrical, 2-storey, 3-bay flatted house built around 1865 and subdivided in the mid to later 20th century. The house features squared and snecked stugged yellow sandstone with polished yellow sandstone dressings. It has a band course at the principal floor and overhanging timber eaves. The openings are chamfered with polished surrounds and stone mullions. At the first floor, there are gabled round-arched windows that break the eaves, decorative timber bargeboards, and window-boxes supported by turned timber uprights and decorative timber balustrades. The rear of the building has harl-pointed rubble, with a 2-storey, single bay harled addition on the outer right, and a whitewashed rubble single storey, 4-bay outbuilding to the northwest, which is shared with the adjacent property at No 23.

The northeast elevation, which serves as the entrance, features steps leading to a round-arched, 2-leaf boarded timber door at the center of the ground floor, adorned with cast-iron fittings, and a small round-arched attic window above. To the outer right, there is a bipartite window at ground level with a consoled window-box beneath a single window centered in the gable above. On the outer left, a 3-light canted window is located at ground level, with a piended roof supporting a window-box beneath a single window centered in the gable above.

The ground floor has 2- and 4-pane timber sash and case windows, while the first floor features replacement glazing. The roof is covered with graded grey slate, and the outer left and right have replacement rainwater goods. There are coped apex stacks on the southeast and northwest, topped with octagonal cans.

The interior was not seen in 1996. The outbuilding has a single window in the penultimate bay to the outer right and boarded timber doors in the remaining bays to the left and right. It also has a graded grey slate roof and a corniced red-brick apex stack, although the cans are missing.

The boundary wall has round-arched rubble coping and is part-rendered random rubble wall along Marine Place.