off the beaten path in Rome

We really enjoyed Trajan's Market and although it's listed in guide books, it's not very crowded with tourists. It was interesting to visit what we would consider to be a modern day shopping mall and the vastness of the site really impressed my husband and me.

I would recommend going across the river into "Trastevere". It's a very medieval neighborhood that I think it often overlooked by the people flooding in to see all the normal tourists attractions. It's a very charming, working-class neighborhood with a fun night life. I really enjoyed just strolling through the streets and enjoying the architecture and or sitting along side at a café watching the people go by.

Well, I guess the ultimate in "old cobblestoned alleyways" would be to walk or bike a portion of the Old Appian Way just outside the city - accessible via metro and bus. Would be able to see the most historic road on earth, catacombs, an old aqueduct, etc.
Can Google search for the website, including a map, if interested.

While there really is no off-the-beaten-path in Roma, there are some less-touristed places. I agree about Trastevere and the Via Appia Antica. I was on Via Appia Antica one morning and had it all to myself for an hour.

There are also lots of neighborhood churches within walking distance of the major basilicas and sights in the Centro Storico, sometimes less than a block away. People line up for the Bocca della Verita and completely miss the church it is joined to, Santa Maria in Cosmedin. Same thing at the Foro Romano - church of SS Cosma & Damiano is right next to it and largely ignored.

If you go to the Aventine Hill (there is the Knights of Malta keyhole and the church of Santa Sabina), there is a nice little park where locals bring their children and the garden has great views of Roma. If you walk down, there is a beautiful rose garden on the way to the main street (Viale Aventino).

Another vote for the Appia Antica: that has been our favorite day in Rome so far. We took a commuter train out to Torricola early in the morning to access it (a sort of harrowing 3/4 mile walk along a piece of busy road from the station) but doing it from Capannelle might be easier. You'd enter it at Casal Rotundo, and can walk it all the way back into central Rome. There are oodles of interesting things to see - ruined tombs, a Roman circus, catacombs, etc - along the way. Bike rentals are also available.

http://www.parcoappiaantica.it

We did Appia Antica on our first visit to Rome. It was lovely. We did the catacombs at San Callixtus (I believe - it was 2008 so my memory is a little fuzzy). And we wandered the tomb of Cecelia Metella. And thre was another area along the road where it looked like they were excavating some ruins - I remember some tile floors...we just wandered in...but this was ages ago.

If you want to do the catacombs - check the times - we got there just when they took an hour or 90 min off for lunch, so we had to cool our heels in the area for awhile. Afterwards, we just wandered up the 'old road' for a ways - I'd love to do a bike tour along it to see more. We caught a bus from near the Colosseum.

...you may also enjoy Osita Antica - easily reachable by train!

Just to second Zoe's excellent advice: if you see a church, go inside - even if it's not in a guidebook. You'll see that they're all different, and most are deserted or nearly so. They are cooler than the outside too (all that stone).

We like to take self-guided walks to explore cities and we have made great use of the book "24 Great Walks in Rome." See if you can pick it up. It has led us to remarkable places and usually we are alone. Another gem is "Rome the Second Time." You might check out the website of the same name.

Why go to one of the world's great cities and avoid the things that make it great? There are a couple of dozen churches worth visiting -- I'd be inclined to research those and see a handful; many are less touristed than say the Colosseum.

San Clemente with its archeological strata is fascinating although hardly untouristed. San Pietro en Vincoli contains Michelangelo's arguably greatest work, certainly one of his top 3, the Moses and is comparatively less touristed. A place that pretty much no one goes is the Aqueduct Park which is reachable on the metro; when my son and I went there about 10 years ago we were literally the only people in the park and it was fun to get up close to the Aqueducts. Ostia Antica on public transport of Rome is amazing and comparatively less touristed; when we were there a few years ago there were maybe 50 people at this enormous site. Villa Julia has a wonderful collection of Etruscan relics; it is the Etruscan museum of Rome. Cervetari and Tarquinia just north of Rome are ancient Etruscan tomb sites and different from each other and very much worth a day trip. Similarly Villa d'Este and Villa Adriana in Tivoli are wonderful; Villa Adriana in particular is a fascinating ruin; in the TV production of Angels in America, 'heaven' was at the large pool at Villa Adriana.

But I sure wouldn't go to Rome and neglect the Borghese, the Pantheon (my favorite building in the world) or the Colosseum and Forum and Palatine.

Besides being a fascinating archaeological site, Ostia Antica is quiet, peaceful area, much of it shaded by fragrant umbrella pine trees. Here's a photo of the crowd at the entrance to Ostia Antica on a mid-day Friday last May.

Thank you, everyone, for your replies. You've shared excellent ideas.
I reread my original question and please know that we will not be ignoring the tourist sites. instead will pick and choose rather than attempting to see them all as we both enjoy immersing ourselves in the culture.

There's a museum called Central Montemartini that's south of the main historic center of Rome. It's an old power plant that now has Roman statues inside. It's definitely off the beaten path even though you can find it in the RS Rome book.

Another fascinating site that is pretty much ignored by tourists is the Baths of Caracalla. We really enjoyed it.