I. M. Pei's 1989 glass pyramid in the Cour Napoléon — initially controversial, now indistinguishable from Paris's image.
From Wikipedia
The Louvre Pyramid is a large glass-and-metal entrance way and skylight designed by the Chinese-American architect I. M. Pei. The pyramid is in the main courtyard of the Louvre Palace in Paris, surrounded by three smaller pyramids. The large pyramid serves as the main entrance to the Louvre Museum, allowing light to the underground visitors hall, while also allowing sight lines of the palace to visitors in the hall, and through access galleries to the different wings of the palace. Completed in 1989 as part of the broader Grand Louvre project, it has become a landmark of Paris and a symbol of the museum.