Art Nouveau was a movement that encompassed more than visual art, extending into packaging design, decorative arts and architecture. Art Nouveau artists, designers and architects wanted to beautify the world. In some small part, at least, they succeeded.
A Russian language LiveJournal blog post by an individual identified as “marinni” titled (as close as I can get with Google Translate) “Windows in the Art Nouveau Style and the mystery of Moscow Windows” is loaded with photographs of glorious Art Nouveau style windows and building facades from various cities in Europe.
There are links at the bottom of the post (before the comments) to Flickr sets, presumably from which the images were drawn.
Can you imagine if this architectural movement had taken hold, and buildings like these defined our cities, instead of the Bauhaus boxes that rise in their stead?