 In March 1944 he graduated from the Politecnico.When the War was over, Castiglioni joined the architectural design practice that his brothers Livio and Pier Giacomo had started with Luigi Caccia Dominioni in 1938.Much of their work was in exhibition design, but they also carried out a number of architectural projects, including the reconstruction in 1952–53 of the , which had been destroyed by bombing in 1943.