 He was attracted by the prosperity of British Guiana and emigrated there in 1860 with a group of Italian priests.Castellani designed a number of prominent buildings in Guyana, including Brickdam Cathedral; Castellani House, once the Guyana Prime Minister's residence; the Brickdam Police Station; and the New Amsterdam Public Hospital.He made alterations and additions to the Church of the Sacred Heart on Main Street (1872-1882), which opened in 1861, for the colony's Madeiran labourers.