9e. Magnificently pompous, crammed with columns, swags and busts of famous composers, Charles Garnier’s 1870s Opéra is open for daytime tours and evening ballet performances. The opulent interior is all marble and gilt with a spectacular if controversial ceiling by Chagall in the auditorium. The Phantom of the Opera haunts the nether regions of the cellars where workmen uncovered an underground lake during the construction.