Haunt of the Phantom of the Opera, the real-life setting for some of Edgar Degas's famous ballet paintings, and still the most opulent theater in the world, the Paris Opéra was begun in 1862 by Charles Garnier at the behest of Napoléon III. Expenses slowed the work down, and it was not completed until 1875, five years after the emperor's abdication. Awash with Algerian colored marbles and gilded putti, it is said to typify Second Empire architecture: a pompous hodgepodge of styles with about as much subtlety as a Wagnerian cymbal crash. The composer Debussy famously compared it to a Turkish bathhouse, but lovers of pomp and splendor will adore it. Look for the allegorical sculpture of Dance on the right-hand side of the facade; it looks ready to leap right off the building.

To see the theater and lobby, you don't actually have to attend a performance: after paying an entry fee, you can stroll around at leisure and view the foyer and have a peek into the auditorium. The monumental Grand Foyer is nearly as big as the auditorium (together they fill 3 acres). After all, this was a theater for Parisians who came to the opera primarily to be seen; on opening nights you can still see Rothschilds and rock stars preen on the grand staircase. If the crimson-and-gilt auditorium seems small, it is only because the stage is the largest in the world -- more than 11,000 square yards, with room for up to 450 performers. Illuminated by a giant chandelier, the fluid pastel figures of Marc Chagall's 1964 ceiling painting contrast oddly with the strong colors below. A small, nondescript on-site museum contains a few paintings and theatrical mementos. The guided tours focus on the building's history and architecture, but don't offer much of a glimpse into the current backstage world. The theater is now the official home of the Paris Ballet, but it usually also mounts one or two full-scale operas a season. (Most operas are presented at the drearily modern Opéra de la Bastille.) COST: EUR6. Métro: Opéra.