The Louvre

The numbers are staggering: 380,000 objects, 35,000 on display, 72,735 square meters of gallery space. If you spent thirty seconds looking at every piece, it would take you over a hundred days without sleeping. Most people come for one painting, take a selfie with it through a wall of other phones, and leave. That's a waste of one of the greatest buildings on Earth.

Before it was a museum, the Louvre was a fortress. Philippe Auguste built it around 1190 to defend against Viking raids up the Seine, and you can still see the medieval foundations in the basement — massive stone walls and a moat, buried under centuries of royal renovation. It became a royal palace under Charles V in the 14th century, and every subsequent king added something, which is why the architecture is such a beautiful mess of medieval, Renaissance, and neoclassical styles.

The Mona Lisa wasn't even famous until it was stolen. In 1911, an Italian handyman named Vincenzo Peruggia hid in a closet overnight, lifted the painting off the wall, tucked it under his coat, and walked out. It was missing for two years, during which the empty wall drew bigger crowds than the painting ever had. Pablo Picasso was briefly a suspect. Peruggia claimed he was trying to return the painting to Italy, but it had been legally purchased by King Francis I directly from Leonardo.

I.M. Pei's glass pyramid, added in 1989, caused nearly as much outrage as the Eiffel Tower had a century earlier. President Mitterrand personally championed it, and critics called it a "gigantic, ruinous gadget." Now it's the most photographed entrance in the world, and the Louvre's annual visitor count has roughly tripled since it was built.