An Entrance to the Paris Métropolitain by Hector Guimard

From www.nga.gov:

A leading figure of the Art Nouveau movement in France, architect Hector Guimard designed 141 models of the Paris entrance to the Métropolitain between 1900 and 1913. He was given the official responsibility for the design of the Métro system, which featured prominently in 1900 at the time of the Exposition Universelle in Paris. Guimard's fame rests largely on the strength of his designs for the Métro entrances. The Art Nouveau movement in Paris also became known as le style Métro and le style Guimard. The architectural forms draw their inspiration from nature, here most notable in the plant stems that support the sign. This coupling of organic form with the new, cast iron fabrication method became a defining characteristic of Art Nouveau architecture. Eighty-six of his Métropolitain stations are still standing, and in 1978 they were registered in Paris as Monuments Historiques.