La Tour Montparnasse, which, at 56 stories, was the tallest building in Europe when it was constructed in 1972, is used primarily as an office building; however, its top two levels are observation decks for tourists. On a nice day, the tower provides a unique aerial view of Paris from the junction of the 6th, 14th, and 15th arrondissements. When traveling to the tower, be sure to visit the world's fastest moving sidewalk, in the Montparnasse metro station!