Built on the site of a former prison, this magnificent 1844-completed church has a richly decorated, colonnaded interior inspired by Roman basilicas. Highlights are stained-glass windows by Charles-Laurent Maréchal and a frieze by Jean-Hippolyte Flandrin. Note that it's closed in July and August.
During the Paris Commune, its bell towers, terrace and ramps were hit by shells fired from Cimetière du Père Lachaise.