> For whatever reason, I think Art Deco ended up supplanting Art Nouveau in US cities.
Art Nouveau was not well fitted for large buildings: it was expensive to build and wasn't easily replicable. Even in Europe, large buildings on Art Nouveau are scarce and were more a proof of concept than a standard way of building. Casa Milá in Barcelona is probably the most relevant example and for sure a must-see.
For a public building you can (pay) to go through, the Musical Instruments Museum in Brussels is a very good example of an Art Nouveau building. (located on Coudenberg at Place Royale)
Art Nouveau was not well fitted for large buildings: it was expensive to build and wasn't easily replicable. Even in Europe, large buildings on Art Nouveau are scarce and were more a proof of concept than a standard way of building. Casa Milá in Barcelona is probably the most relevant example and for sure a must-see.