 His buildings are typical of the eclecticism of the time, designing in both Gothic Revival style and a so-called neo-Renaissance style of classicism, with heavy ornamentation as well as heavy use of colour in interiors but also occasionally in facades, as for instance with his House of the Estates, Helsinki (1891).The semi-circular Rotonda (1902–07), Gustaf Nyström's design for the extension to C.L.Engel's neoclassical Helsinki University Library (1845), demonstrates both an outwardly stylistic continuity with the original - albeit the pilasters have not classical capitals but reliefs, made by the sculptor Walter Runeberg, personifying the sciences - whilst also employing modern techniques in the Art Nouveau interior