The original square stone building of the Castle Mona Hotel consisted of two three storey wings front and back joined by a two storey 'link' of similar plan size. The flat roofs of the wings are concealed behind parapets decorated with roundels and garland motifs except over the entrance where castellations indicate the substantial protruding porch with its columns and wrought iron balustrade to a flat roof. The central link has a slate pitched roof visible through a castellated parapet. The well proportioned rectangular windows decrease in their vertical dimension with each succeeding storey but receive the same treatment on all elevations of the structure. The building is crowned by a circular castellated tower rising from the rear of the main facades toward Douglas bay. A recent extension to the sea creates a large terrace with wrought iron balustrade on the roof of the single storey alteration which is fronted by shops onto the main pavement of the Cresent. No interior inspection has been made. Although the developments of the promenades at Douglas has detracted from the siting of Castle Mona by leaving it behind the main visual facade, the building is still impressive both for its quality of architecture and its historic significance as the early residence of the Duke of Atholl (Governor General of the island 1793-1830).