And the middle of the City of Light is the Seine River and the two small islands that sit within its flowing waters. Those islands are the heart of Paris tourist activity.

Visitors come for the country's most famous ice cream shop, lining up beside well-dressed children with balloons tied to their wrists. They come for the hulking Notre Dame Cathedral, to point cameras at kneeling worshipers. And they come simply because it is the middle of the city. It is easy and it is safe.

But head north or head south and you begin to make a choice about Paris. An age-old choice.

To the north sits the city's Right Bank and to the south its Left Bank. Both are equally Paris _ drenched in history, soaring architecture and sense-stirring neighborhoods _ but most people who know the city well enough to choose one side as their own do so.

Unlike most cities, where race or class drives geographical allegiance, here the choice is imprecise; it comes from a feeling, a sense, a memory, an essence. Ask a local whether someone is Rive Droite (Right) or Rive Gauche (Left) and you might hear about how the differences between them have narrowed or about how they have changed _ the Left was edgier a generation ago; now it's the Right _ but you will not hear that the question is irrelevant.

The differences between the banks are subtle, and if you confine yourself to the usual tourist haunts, you'll miss them.

"I feel more myself in the Right Bank," my hotel receptionist told me. "In the Left Bank, I feel badly if I stay too long."

It's not that Parisians refuse to visit the other side as they once did; the Right-leaning hotel receptionist, unfortunately for him, works on the Left Bank. But where you lay your head counts and probably always will.

Odile Hellier, owner of the Village Voice, a handsome, tidy English-language Left Bank bookstore, lived in six Right Bank arrondissements _ the Paris version of a neighborhood _ before settling in the Left.

"I never felt at home, really," Hellier said. "It's crazy. It's all Paris. But I would go out in the street and it wasn't my thing."

The Louvre and Arc de Triomphe sit on the Right Bank; the Musee d'Orsay and Eiffel Tower are on the Left _ but who cares? Those stops belong to the world as much as to Paris. Visitors who push past the typical attractions will likely find a piece of themselves on either the Right or Left Banks. Then they, too, can pledge affection.

For decades, the Right Bank was known as home to the bourgeois and old money, but that image has been turned on its head. While the old money is still there, today's devotees of the Right Bank praise its lively, youthful neighborhoods.

Best known are Montmartre, at the far northern end of the city, and the Marais, on the Seine's north edge. While Montmartre, especially its stone white Sacre-Coeur basilica, is overrun with tourists, the Marais retains a relatively local flavor. It is the traditional home of the city's gay and Jewish populations, and the place for boutique shopping, people-watching and the city's less heralded but still fascinating museums _ the Pompidou, the Picasso museum, a hunting and nature museum and the Jewish Art Museum.

The Marais buzzes late into the night and abounds with good, cheap food, such as crepe outpost Breizh Cafe or Chez Hanna, which claims to serve the "best falafel in the world" (layered with hummus, roasted eggplant and shredded cabbage, it may not be the best, but it is up there). The Marais moves with an easy grace, and you're just as likely to see locals in the art galleries or bars as you are to see well-dressed tourists.

Anne Leguy, 48, was a proud Left Bank resident for 13 years, living in the St. Germain neighborhood immortalized by authors, thinkers and poets. When she arrived, her streets were abuzz deep into the evening. But by the early '90s they had become "too bourgeois," she said. Leguy now lives with her family in the Marais and can't imagine living anywhere else. She holds no grudge against her old home on the other side of the river.

"It's not like you care if it's Left Bank or Right Bank if it's a place you want to go," Leguy said over the veal tagine at Chez Pierro, a Marais bistro so narrow that tables must be maneuvered for anyone to sit. "But I can't say that is true for where you have your flat."

Right Bank life keeps buzzing well past the Marais. In the 9th arrondissement, Rue des Martyrs closes to cars on Sunday mornings and transforms into a wonderful street market where you find few tourists fumbling with guidebooks. Instead there are street musicians playing for change, families shopping for dinner among the roasting chickens and fish laid across melting ice and long lines into the patisseries, where the baguettes or pains au chocolat are warm, fresh and perfect.

Artists displaced by rising property costs in the ...