ParisThe distinctive, ornate, Art Nouveau metro entrances designed by Hector Guimard are a famous synonym for Paris's metro. Some are lost but 88 of them still exist [
parisinconnu.com]. RATP gave reproductions to the subways in Chicago, Lisbon, Mexico City and to the Museum of Modern Art in New York, and an original one to Montreal [
metrodemontreal.com].
Photo: The entrance at Abbesses station, designed in 1910, is one of the larger ones.

The elegant metro stations in Paris are mostly column-free vaults and look similar throughout the system, which was inaugurated in 1900. Everything has been refurbished for the 100th anniversary.
Photo [
Mike Nguyen]: Cité station on line 4.

An enjoyable architecture has also been implemented in Paris's newest RER stations as well as in the new driverless metro line 14 (Météor).
Photo: Magenta RER station with its interesting lighting.