I somehow missed this during my three trips to Paris since 2000. It’s one of the Metro entrances—called bouches (mouths)—to the Palais Royal-Musee du Louvre station which sits on the rue de Rivoli side of the Louvre and in front of the Palais Royal. It was commissioned to celebrate the centennial of the Paris Metro in 2000 and is called “Kiosk for Sleepwalkers.” The artist is Jean-Michel Othoniel, a young French homme (man). 
The sunken staircase entry into the station is covered with two open cupolas (one for day, they say, and one for night) outlined by 800 Murano glass beads in seven colors—all supported by an aluminum frame. The staircase is surrounded at street level by a low barrier wall composed of small aluminum circles, some filled with colored glass. It is very beautiful, as you can see, especially in the sun.
Of all the redesigns of stations in the recent years, this one is particularly relevant because the original stations designed by Hector Guimard were classified as Art Nouveau. Blending architecture with decorative work, his curvy plantlike ironwork decorated the 141 original Metro entrances in 1900 and only a few survive; one is the Cite station near Sainte-Chapelle. The Museum of Modern Art in New York managed to buy one of the old station entrances before Paris realized their future worth. 
Over the years, the network has grown to almost 300 stations (the 298th Tolbiac station will open in the 13th arrondissement in June). Not all of the bouches are fancy. 
Some are indiscreet stairways disappearing into buildings or sudden stairwells appearing in the pavement. But all are identified by some type of Metro sign and some still display the original light fixture from 1920 atop the red Metro sign.Here are some pictures showing the different styles.
BTW, the Metro maps have a special coating so that oils from fingertips don't corrode the surface. Before the city did this, there used to be gaping holes on the popular sites on the maps. Interesting, huh?
