What would possess Joanna Goddard to open her home to people she doesn't even know? The opportunity to stay in theirs! Welcome to the wild world of house swapping, the best deal in travel for those willing to make a trade.

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Joanna and her sister in Michael and Sabrina's San Francisco apartment

I live in New York. But I also have flats in San Francisco and Los Angeles, and I keep a condo in Miami, a ch teau in Switzerland, and a pied- -terre in every Paris arrondissement. You see, I'm a house swapper. As an avid traveler with a (very) limited budget, I've discovered that trading apartments with people I meet on the Internet they stay in my place while I'm crashing at theirs is an excellent way to save money on vacation. In fact, after seven successful trades, I've become addicted to swapping and have made converts of my boyfriend, Alex; my sister, Lucy; and my mom, Jean all of whom have accompanied me on trips. Sometimes I can't imagine ever shelling out cash for a hotel again.

My virgin house swap was, fittingly, in the city of love: Paris. My mom and I had long dreamed of visiting together, but our lack of funds forced us to keep postponing the trip. Finally, in 2006, I decided that enough was enough. Instead of being scared off by pricey hotels and break-the-bank exchange rates I went on craigslist.org to look for an apartment swap. After I clicked on the Housing Swap link and typed in Paris and September, the ideal place popped up: a one-bedroom apartment owned by Olivier*, a 30-something software company founder who wanted to visit Manhattan with his girlfriend. His home looked decent in the photos, and the central location on the Left Bank couldn't be beat. The timing also worked out perfectly, as we both wanted to travel to each other's cities in the first week of September. I e-mailed him photos of my apartment, and after a few polite exchanges, we were all set. I put my house keys in the mail, and I received Olivier's keys a week later. I couldn't believe how easy it was or how free.

Two months later, my mom and I were on Olivier's tree-lined street, which was so beautiful it was almost clich d: chic couples strolling arm in arm, children playing soccer, a wine bar on the corner. Olivier's fifth-floor apartment was equally charming, with huge windows overlooking a sunlit courtyard, and a cute kitchen where Olivier had left us a bottle of wine. You can tell a bachelor lives here, my mom said with a laugh when she noticed the mattress on the floor in lieu of an actual bed. The mattress, however, was surprisingly cozy and proved to be a perfect spot for reading maps in the morning and Voltaire at night.

House swapping not only allowed us to drop into the city, but into a Parisian lifestyle, too. I often feel like an outsider when I visit new places, and I observe with an anthropologist's fascination how the locals go about their days. I'll mimic their eating habits, gestures, and pastimes until it's time to go back to my hotel. Staying in Olivier's apartment, however, enabled me and my mom to slip into his life. We bought our morning espresso from the neighborhood caf he had recommended. We roasted a chicken in his kitchen one night and ate at a nearby bistro the next. We chatted with the neighbors on the stairs, fiddled with the leaky sink in the kitchen, and read Paris Vogue on the sofa. And, like Olivier, we felt Parisian at least for a week.

A born-and-bred control freak, I've always chosen my hotels after scouring magazine articles and grilling my friends for recommendations. When you book a room that way, you know what you'll get and you pay for that reliability. House swaps, however, force you to take a leap of faith. There's usually no contract or security deposit. And you never receive a reservation confirmation. When I arranged my Paris swap, I had to trust that Olivier was telling the truth about himself and his apartment. I was a bit nervous on the flight to France, with images of serial killers, con artists, and rats flashing through my mind. But after a few glasses of wine, I got over my fears. House swappers quickly realize they need to be open-minded and have a sense of humor about the unexpected inconveniences that can pop up. And, browser beware: Some swaps do come with surprises.

This past May, my sister and I traded places with Michael, the owner of a club in San Francisco, and Sabrina, his girlfriend. The second-floor apartment was gorgeous, with hardwood floors, a flat-screen television, and a large, comfortable bedroom. And I especially loved the claw-foot tub a real treat for a Manhattanite. Michael and Sabrina had also left us free tickets to concerts and recommended we eat at Patxi's, a deep-dish-pizza restaurant they love down the block. On a sunny Saturday, we purchased fresh vegetables at the farmers market and tried out a few recipes we found while flipping through their cookbooks.