Between Montmartre and the Grands Boulevards, this area of the 9th is ignored by the majority of tourists, who transit undergound between Montmartre and the center of Paris, but it is a discrete, authentic Parisian neighborhood where people live and work, with some of the best that local Paris life has to offer as well as some hidden gems for well-informed visitors. The only exception of course is Pigalle, which is world-reknown as the major Paris red-light district, separating the 9th from Montmartre.
Among the hidden gems that you will want to appreciate if you stay in this neighborhood are the Musée de la Vie Romantique, with its seemingly secret English-style garden, the rue des Martyrs with its wide selection of specialty shops, the Gustave Moreau museum, and the Place Gustave Toudouze for a delightful lunch outside on the square. For something a bit more sexy, you have the Moulin-Rouge cabaret as well as the Museum of Eroticism.
The neighborhood is also well-endowed with famous theatre venues, such as the Folies Bergere and the Paris Casino.