If you want to eat at the best restaurants in Rome, you need to get out of the touristy center. And that's when most travelers to Rome balk.

But they don't have to. As overwhelming and confusing as Rome's public transport system can seem, there's only one bus you really need to know in order to hit nearly all of Rome's best food neighborhoods. Ladies and gentlemen… let me present:

The number 3.

Now, there are many things I don't like about the #3 bus. It makes lots of stops. It gets super-crowded around rush hour (avoid it from about 7am-9am and 5pm-7pm). And like any bus in Rome, it can be erratic, sometimes coming every 5 minutes, sometimes every 20.

But I find myself hopping on it again and again, just because, for the price of one euro, it takes me to nearly all of my favorite restaurants.

Update, 9/2012: The #3 bus is now a… #3 tram! (It actually started out that way, so I guess it's going back to its roots). The good news: There is now much more room, making the ride much more comfortable. And trams are fun. The bad news: The tram now stops in Testaccio, at Piazza Ostiense. From there, you have to switch to the bus to carry on to Trastevere. But if any neighborhood is worth stopping in, food-wise, it's Testaccio! 

The #3 starts (or ends, depending on your point of view) at Thorvaldsen, a stop in the Villa Borghese right near the Galleria Arte Moderna. It then hits:

• Parioli, a well-heeled neighborhood that's starting to come alive with equally-upmarket restaurants
• San Lorenzo, a student quarter that has excellent, cheap trattorie and hip, grungy bars alike
• the Porta San Giovanni down to the Colosseum
• the Celian and Aventine hills
• Testaccio, one of Rome's best food neighborhoods for cheap, traditional cucina romana
• Trastevere, another great food neighborhood with both higher- and lower-end dining

But it's not just food that you can explore by hopping on and off the #3. There are sites, too—and (bonus) a lot of them are the slightly more off-the-beaten-path and, in my opinion, rewarding kind.

So… let's get on the #3 and see where, exactly, it takes us. (The neighborhood names are rough generalizations; I've just used them to make everything easier to visualize).

Parioli: Thorvaldsen to Viale Regina Margherita

Eat: End with dinner in this 'hood if you're looking for something a little more upscale and creative. The top restaurant is probably All'Oro, a pricey but excellent Michelin-starred restaurant serving up creative dishes like risotto with artichokes, vanilla and roasted calamari (they offer a tasting menu for 55 or 70 euros); it's a 10-minute walk from the Rossini stop. For something more moderately-priced, check out Anatra Grassa, which serves up Venetian-influenced food (get off at the first stop on V.le Regina Margherita after Buenos Aires). And if you just want a break from Italian, Duke's California Bar & Restaurant offers Angus steaks, sushi, foie gras, and other not-so-easy-to-find foods in Rome.

Do: From the first three stops on the line (Thorvaldsen, Galleria Arte Moderna and Aldrovandi), it's easy to stroll around the beautiful Villa Borghese, taking in museums like the Galleria Arte Moderna, Villa Giulia, and, of course, the Galleria Borghese. From Liegi, the 5th stop, you can explore the Villa Ada, one of Rome's largest parks, and walk to the Catacombs of Santa Priscilla, one of Rome's least-visited but most-rewarding catacombs.

San Lorenzo: Policlinico to Piazza di Porta Maggiore 

Eat: Gritty and graffiti-filled, San Lorenzo couldn't be more different than Parioli. And since the diners around here tend to be a little on the more money-saving side (read: lots of students), the restaurants are much cheaper, too. One of my favorite traditional Roman spots is Trattoria Pommidoro, which has particularly good game meats, along with pastas (I love their pasta alla gricia); I've also heard good things about Tram Tram, a traditional and well-priced favorite decorated with pieces of, you've got it, a vintage tram. On the trendier and much more expensive side, there's Pastificio San Lorenzo, a restaurant located in an old factory that's an art gallery by day, serving up gourmet Italian dishes. Top it off with some chocolate at Said, a chocolate factory that's been around since 1923. And all of these eateries are a stone's throw from the Reti stop.  

Do: Get off at the Verano stop to visit the Basilica of San Lorenzo fuori le Mura (below), a gem of an ancient church, and its atmospheric cemetery. At the Piazza di Porta Maggiore stop, check out Porta Maggiore, a monumental 1st-century Roman gate, and the huge 3rd-century Aurelian Walls. Don't miss the Baker's Tomb, an extremely unusual—and unusual-looking—tomb of an ancient Roman baker, honeycombed with holes that it's thought symbolize units of grain.

Esquiline: Santa Croce in Gerusalemme to Colosseo    

Eat: On the higher end, Agata e Romeo is a Michelin-starred (and very expensive) Roman restaurant just a 10-minute walk from the Manzoni stop. For something more moderate, check out Tempio di Iside, one of the best seafood restaurants in Rome (get off at the first Labicana stop). But my favorite pick has to be Da Danilo, a fantastic, moderately-priced Roman trattoria just a 5-minute walk from the Manzoni stop. Whatever you do, don't miss their carbonara (above). Finally, after visiting the Basilica of San Clemente (see below), make a stop at Ciuri Ciuri for some of Rome's best cannoli and other Sicilian goodies (right at the 2nd stop on Labicana).

Do: Aside from, obviously, seeing the Colosseum, visit the Basilica of Santa Croce in Gerusalemme, a church dating back to the 4th century that has a number of bizarre relics, including thorns from Christ's crown of thorns, wooden pieces of the cross, and (they say) the bone of the finger of St. Thomas that he put in Christ's wounds after he rose from the dead. Get off at Porta San Giovanni to stop at the Basilica of San Giovanni and the Holy Stairs. Or (my favorites) get off at the 2nd stop on Labicana to pay a visit to the Basilica of San Clemente, a 12th-century church built on top of the 4th-century basilica built on top of ancient Roman ruins (incredibly, you can descend down to see all of the layers), and to the nearby Church of Santi Quattro Coronati.

From the Celian hill to the Aventine

Eat: If it's the weekend, get off at the 1st Aventino stop and walk along the Circus Maximus to the Campagna Amica food market, a great place to sample local foods and even enjoy a cheap, delicious lunch. Just around the corner, pop into Cristalli di Zucchero, home to some of Rome's best gourmet (and not just Italian) sweets, pastries and macaroons.

Do: Get off at the Parco Celio site to (you guessed it) stroll through the lovely Celian park (in summer, you can catch jazz concerts here), as well as to check out the Case Romane; if you cross the street, you can access the Palatine and its ruins of the Roman emperors' palaces. At the 1st Aventino stop, take in the Circus Maximus or stroll around the Aventine hill, one of Rome's oldest and prettiest residential neighborhoods. Don't miss the incredible ancient basilica of Santa Sabina, the lovely Garden of Oranges with its view over the city, or everyone's favorite keyhole: the one at the Piazza of the Knights of Malta, where you can see the Knights' property, Rome, and St. Peter's—three countries in one glance.

Testaccio: Porta S. Paolo to Emporio

Eat: Testaccio is one of Rome's best, most authentic neighborhoods for food. Make the most of it. Check out the market at Piazza Testaccio, where locals go to buy their produce (along with shoes and sundry items). Right on Via Marmorata, where the #3 stops (twice), grab a Sicilian pastry or cannolo at Sicilia e Duci (above) or some (pricey, but delicious) cured meats or specialty cheeses at foodie favorite Volpetti. If you're in the mood for a full meal, beeline to Da Bucatino (one block from Via Marmorata) for classic Roman fare, Nuovo Mondo or Da Remo for pizza, or my latest favorite, Flavio al Velavevodetto, which serves up excellent food for moderate prices.

Do: Get off at Porta San Paolo to check out the pyramid of Caius Cestius, a tomb built to a magistrate in the 1st century B.C. that looks like a bizarre little piece of Egypt among Roman traffic. From here, you also can explore the Protestant Cemetery, resting place of expats like John Keats. Take one of the stops on Marmorata to head to the MACRO, a contemporary art museum in a reconstituted slaughterhouse.

Trastevere: Porta Portese to Staz.ne Trastevere

Eat: Like San Lorenzo and Testaccio, Trastevere is full of well-priced, good-quality Roman restaurants—but it's also got its share of tourist joints, so go prepared. Get off at the Porta Portese stop and walk north to enjoy delicious pasta, served fresh in the pan, at Taverna Trilussa, or grab cheap, traditional pizza at Ai Marmi (above). Le Mani in Pasta, a surprisingly elegant hole-in-the-wall, is another local favorite, while L'Asino Cotto serves up creative Mediterranean fare. On the highest end, Glass Hostaria is a super-modern (and expensive) Michelin-starred restaurant in the heart of Trastevere.

Do: If it's a Sunday morning, check out the goods (and junk) at Porta Portese, Rome's biggest flea market. Otherwise, get off at the same stop and walk over to the Basilica of Santa Cecilia, which boasts 13th-century frescoes by Pietro Cavallini, a sculpture by Maderno of Cecilia's incorrupt body as it was found in 1599, and excavations of two ancient Roman houses below that you can visit. Further in the heart of Trastevere, check out the Basilica of Santa Maria in Trastevere along with the Villa Farnesina, home to some of Raphael's loveliest frescoes.