John Henderson, 1841; library addition J Sim, 1888. Distinctive neo-classical 2-storey block with 3-bay entrance front. Fine channelled sandstone ashlar to front, squared and snecked to rear. Deep base course, band course above 2nd floor, cornice and parapet. Raised and architraved margins. Pilaster wall ends.
E (ENTRANCE) ELEVATION: central Ionic portico in antis, doorway with corniced head, "MUSEUM" in gilded lettering beneath cornice, panel above at 1st floor with carved key pattern within. Bays flanking window at ground with corniced head and intricate geometrical glazing: panel above each bay at 1st floor with carved key pattern within. Full-width frieze with key pattern in upper band. Parapet with 4 dies and raised section to centre with panels and cornice.
N ELEVATION: 4 bays of original block to left; symmetrical, windows with corniced heads and intricate geometrical glazing, panels above at 1st floor and bronze key pattern within. Slightly advanced library entrance to right; 3 bays with Ionic portico in antis, pilastered doorway with rectangular fanlight, 2-leaf doors, horizontal banding above and recessed pilastered panel at 1st floor with key pattern and paterae. Pilastered bays flanking with full-height banded rustication, pilastered window at ground, horizontal banding above and recessed pilastered panel at 1st floor with key pattern. Full-width frieze with key pattern in upper band. Parapet with 4 dies.
S ELEVATION: 4 bays of original block to right; 3 windows with intricate geometrical glazing, window to right blocked, 4 small windows centred above. Library extension to left, slightly advanced, 4 bays at ground floor, parapet with corner dies.
W ELEVATION: blank brick wall with raised stone wallhead. Modern steel fire escape with door at 1st floor.
Multi-pane glazing at ground floor to front, 4-pane to library extension. Grey slate piended roof.
INTERIOR: main exhibition hall with galleried 1st floor, diamond patterned cast-iron balustrade around rectangular opening. Boarded walls, plaster panels with decorative louvres and cornices above dado at 1st floor. Shallow barrel-vaulted ceiling with rooflights in panels to N and S. 10-step flight and round-arched entrance to additional hall to W. Rooms to W in library extension now offices and exhibition hall, cast-iron columns as roof supports, decorative cornices.
BOUNDARY WALLS, GATEPIERS AND RAILINGS: low coped ashlar boundary wall to S, E and N with square section corner piers and gate piers to E, wrought-iron gate with geometrical and key patterns. Cast-iron railings to NW on Museum Street enclosing garden. Part of the stone balustrade of Montrose Suspension Bridge (1828 - 1928) is erected in the garden.