Note that on the 1st Sunday of the month, state museums in Italy are free (including attractions like the Colosseo, Forum, etc). The lines will be unimaginably awful.
GMt, I believe the OP says that she has another day set aside for the Vatican.
Even w a separate day set aside for the Vatican, I still wouldn’t do it in the summer time-- ack!
I also used Caitlin Miller for a private tour and she was great. She gets booked quickly. If you only have one day, it is most efficient to go with a private tour.
Is Caitlin Miller an independent tour guide - I searched and can find references to her name but no website
No disagreements with anything above - you’re getting great comments and advice! I thought I might further summarize re the museums. Art history is my avocation - all of three “majors” above mentioned (Borghese, Capitoline, Museo Nazionale Romano - Palazzo Massimo alle Terme) are spectacular with their own “specialties”.
The Borghese is probably the closest to a “standard” art museum with painting and sculpture collection to die for. The timed tickets allow ONLY a two hour visit. You will be kicked out at the end of your time. I had no trouble seeing everything and returning to my favorite works in this time frame. So, if you are setting an itinerary for your visit, the Borghese timeframe is easy to define.
I think it is worth spending a little time on the websites or a library Rome tour book to see the offerings at the museums. You may have specialized interests we aren’t aware of - for example, if you like Roman sculpture, then it would be Capitoline or fresco - then Palazzo Massimo alle Terme.
By the way, there are still some less frequented, but spectacular painting collections. I won’t mention these to avoid further confusion, unless someone wants further recommendations. I also agree that the Vatican Museums are over-run. Wonderful collection, but… Also, to get to the Sistine Chapel, you go through the Museum. We visited once with a special evening time slot - don’t know if they still offer this, but the crowds were minimal. Only parts of the museum were open, but this was satisfactory for most people. For me, we went in the evening, then again when the rest of the museum was open.
Use a tour guide for the vatican. Bypass lines and get much more info. There are areas set aside just for tour groups with displays that explain the layout and history of Vatican.
Coliseum/Forum and outdoor areas over a museum. Make sure to get in tour of Coliseum–you can get a guide right outside with no problem (and doesn’t cost much over regular ticket price). You have to or you’ll be standing in lines for half your day. Having a private tour guide is great advice.
Watch your wallets! Pickpockets are rampant. Get your husband a pair of travel pants with some pick pocket proof pockets (say that 4 times fast). Wear a waist belt under your clothes.
rightfit - search her name with Rome tour guide. You can see her linkedin profile too. I will PM you.
Yes, Caitlin is independent. She’s a young American woman.
I agree with many of the previous posters. If you really want to go to a museum, the Borghese Gallery is amazing (and you need to order your tickets in advance). However, since you will tour the Vatican you might want to spend the day walking around Rome. It’s very walkable, and there are wonderful works of art you can see as you walk around. The Pantheon, Piazza Navona, Spanish Steps, and the Colosseum were highlights of our trip. Also, I agree that with just one day a great tour guide would be very nice.
I agree with the recommendations of the Borghese Gallery and the Capitoline Museum – both are amazing, and both are far less crowded than the Vatican museum. For whatever reason, I was a little disappointed with the Forum. You really have to use your imagination to envision anything like what it used to look like. (Maybe the fact that it was about 100 degrees that day also had something to do with it!) The Pantheon is magnificent, and I wouldn’t miss the Colosseum either.
Colosseum and the Roman Forum are incredible to see. Be careful when joining up with random tour guides outside the gates. Many have little knowledge about the site. But you will be able to skip the line for about €15. The Spanish Steps were closed for renovation when we visited in March. I haven’t seen anything that indicates they have reopened. It’s a tremendous walking city and most churches are open during the day. Each is unique in design and artwork.
WHen we did a cruise and had one day we did “Romeinlimo” (romeinlimo.com) and they packed as much as possible in that one day. Check them out.
I think walking is the way to go in Rome. You could do the Borghese in the morning and still have time to walk and walk but honestly, the ancient sites will be more worthwhile if you only have one day. And I love the Borghese.
My two top picks would be The Forum and Palatine Hill and the Jewish Ghetto. They are very close to each other and you will get a great sense of the historic sweep of the city as you will see the ancient, the Medieval and the Renaissance all mixed together. Stop for coffee outdoors on a piazza and people watch. 2 resources for self-guided walking tours are the book Romewalks http://us.macmillan.com/romewalks/anyamshetterly and Rick Steves’ audio tours https://www.ricksteves.com/watch-read-listen/audio/audio-tours/italy.
Enjoy!!
When do we get to talk about FOOD? 
Agree about choosing Pantheon, it is awesome, since you are going to the Vatican already, which really is the museum you want to see anyway. For my money, Michelangelo’s Pietà in St. Peter’s is the most beautiful single piece of art ever created.
Have a great time! And Frascati and Burrata!
Please talk food 
I’ll talk food. The only thing I’ll add to the walking tour suggestion is to use gelato as fuel. We did 5-gelato days while walking through Rome.
Exhausting but great!
I remember we could have a meal with either a bottle of wine or bottle of water apiece included in the price. I ordered water and H ordered wine with the meal. He got sick the next day and I was fine. I ordered takeout chicken soup the next day after I had my early dinner. The restaurant seemed very surprised by my request for takeout chicken soup but eventually sold it to me so I could give it to H for dinner.
Learn difference between osteria, trattoria, restaurant. Lots of different levels of dining that go by different names–don’t bypass the cheaper dining establishments because you didn’t know their names! A restaurant is fine dining.
Linen pants work great in the heat and as Fernando Lamas would say they look marvelous.
As for food - I’ll recommend Il Nido Del Pettirosso - you’ll need a reservation.