This is a wholly subjective list of some of my favorite, lesser-known sights, museums, monuments, and experiences in Paris. I have a pretty broad definition of "lesser-known" that includes anything not on the main Top 10 list.
That means some of these sights may be truly famous (just a shade less so than, say, the Louvre or Notre-Dame), while some of them will be pretty obscure, places I've come to love in a lifetime of returning to Paris.
★★ Centre Georges Pompidou (Pompidou Museum) - A stellar collection of modern art in a giant building that must have looked cutting edge in the 1970s and bears a striking resemblance to a hamster's Habitrail set... » more
★★ Sainte-Chapelle - A stained-glass jewel box of a church that glows in architectures of light, hidden away in a courtyard surrounded by government buildings on Île de la Cité, just blocks from Notre-Dame... » more
★ Musée de l'Orangerie - One of my favorite hidden sights in Paris, packed with Impressionist paintings and preserving in its basement two rooms fitted with 360 degrees of Monet waterlillies... » more
★ Père-Lachaise Cemetery - It's not just the scores of famous graves—Oscar Wilde, Chopin, Edith Piaf, Gertrude Stein, Jim Morrison—it's a stunning beautiful cemetery, crammed with stone monuments laid out over rolling, forested hillsides... » more
★ Musée National du Moyen Ages - Thermes de Cluny - This museum to the Middle Ages in Paris—including the famous medieval "Lady and the Uncorn" tapestries—is partially installed in the city's ancient Roman baths... » more
The Institut du Monde Arabe - Close-up views of the Seine and the buttressed backside of Notre Dame from a funky, post-modern building (bonus: shows of Middle Eastern culture and a tented Arab bazaar out front)... » more