Wilhelm Westhofen, artist and engineer, was a member of the (British) Institution of Civil Engineers. In February 1890 he published a comprehensive paper on "The Forth bridge" (the cantilever railway bridge over the Firth of Forth in Scotland) in the journal Engineering (71p). On 6 August 1892 he was appointed as engineer in the Public Works Department of the Cape Colony, a position he held until he retired on pension in 1904. In 1903 he submitted to the Cape Parliament his Report on the proposed construction of a fishing harbour at Kalk Bay. During 1905-1907 his address was Southfield House, Plumstead. He seems to have maintained some connection with the Public Works Department until 1910.
In 1902 Westhofen became a foundation member of the Cape Society of Civil Engineers and was elected joint vice-president of the society. Having served in this capacity until 1905 and as a member of council for the next year, he was elected president in 1907. During these years he delivered two papers that were published in the society's Minutes of Proceedings, "Materials for bridge construction in Cape Colony" (15 June 1904) and "The erection of the Colesberg road bridge" (11 July 1906). He was still a member of the society's successor, the South African Society of Civil Engineers, in 1913.
Westhofen was a foundation member also of the South African Association for the Advancement of Science (and his wife an associate member). He served on its council as honorary treasurer from the association's beginning in 1902 to at least 1905. At its first annual congress, held in Cape Town in 1903, he contributed a paper on "The irrigation question in South Africa" (Report, 1903, pp. 373-382), in which he blamed the slow progress in the development of local irrigation schemes on the lack, until recently, of political support and capital. He was a member of the South African Philosophical Society from 1892 to at least 1898. In the latter year he presented a single snake to the South African Museum in Cape Town. His artistic talents found expression in the illustration of three books: The Cape Peninsula: being pen and colour sketches described by R?n? Juta and painted by W. Westhofen (Cape Town, 1910), Six South African scenes and verse (Cape Town, 1925), and Twelve South African scenes and verse (Cape Town, 1925). He also held exhibitions of his art. In 1914 he was appointed as one of the trustees of the South African Art Gallery, a position from which he resigned in 1925, the year of his death.