Ams­ter­dam offers a wealth of urban plan­ning and archi­tec­ture from the pre- and post-war peri­ods. The south of the city in par­tic­u­lar is a ver­i­ta­ble open-air muse­um of mod­ernism.  Most of the build­ings were designed by archi­tects of the expres­sion­ist Ams­ter­dam School, but there are also some impres­sive exam­ples of Func­tion­al­ism — most notably the build­ing of the Open-Air School by Jan Duik­er. In the 1950s, Func­tion­al­ism was replaced by Struc­tural­ism. The best-known icon of this school was cre­at­ed by Aldo van Eyck: an orphan­age for 125 chil­dren. Twen­ty years lat­er, Her­man Hertzberg­er fur­ther devel­oped the typ­i­cal spa­tial con­struc­tion of struc­tural­ism in his design for the Apol­lo Schools.