Rome- Colosseum & highlights?

If you are going next month, you still have some options for buying tickets directly from the source (that is to say, not through tour companies or resellers). Tickets available through https://ticketing.colosseo.it open up exactly 30 days in advance, so tickets for 8:30 AM on June 1 will open at 8:30 AM tomorrow (Italy time). There are some good guides on reddit for how to get tickets through the official website.

As far as I'm aware, the general admission tickets don't usually sell out, and you can also buy general admission tickets on the day you want to visit if you don't mind waiting in line. The line can be super long, though. And the special tickets (for the attic, which is the upper levels of the arena, or the underground, which is the part that used to be below the arena floor) are only available to be purchased in advance through the website, and they often sell out very quickly once they become available, like within minutes.

I recently visited with Attic tickets and it was great! I loved taking the elevator up to the upper levels. They had great views, and the second level area has this little staircase leading down to a gated window--it was a perfect spot to just listen to an audio guide in the shade while looking down at the rest of the arena. Thanks to the limited number of tickets, it was also positively peaceful compared to the rest of the arena, which was crammed full of people!

You can try to get attic/underground tickets through a reseller or a tour, but I've heard it's a risky thing to do. They might sell tours without having actually obtained enough tickets and then cancel on you.

As for other recommendations, one thing I wish I'd known is that parts of the forum (access to the forum is included with most Colosseum tickets) are only open on certain days. I was so sad when I realized that I couldn't go inside the Curia Julia because it's only open on Saturdays, Sundays, and Mondays! I would say the forum also takes more pre-visit research than the Colosseum to really enjoy. We used the Rick Steves audio tour of the forum, but found it more confusing than most of his tours because so much was inaccessible due to construction/restoration and we kept having to seek out alternate paths or skip things, and I sometimes felt a little confused about what I was seeing. If I had a better sense of what I was looking at before stepping foot in the place, I think I would've enjoyed it more.

Good feedback from Mae.
I'll just mention that I'll personally advise booking a guided tour that includes the Colosseum, Forum and Palatine. The Colosseum's own website doesn't offer one of these so you'll need to use an independent company (Through Eternity, Roman Guy, etc.). The Colosseum is easy enough to understand on your own with an audio guide or advance reading but the other two sites are important, much more complex, and really benefit from a human guide to shepherd you through and explain what you're looking at.

I would not put the energy into landing any tours which include the Colosseum's underground. They're very difficult to get, don't spend a lot of time in that part, and you can see down into it from point above. Mae had a positive experience with the 'attic' and I'm reading lots of glowing reviews of that piece so you might look into it but otherwise consider a 3-site tour. They generally run between 3-4 hours.

Other highlights, depending on interests and time:
Galleria Borghese: advance reservations are mandatory and sell out quickly

Pantheon: also has an entry fee and advance reservations although walk-up tickets are possible

Piazzas: Campo di Fiori, Navona, del Popolo, del Campidoglio, tiny Piazza Mattei... Skip Piazza Venezia as there's massive construction in that area.

A list of churches too long to include but Santa Maria Maggiore, San Clemente, San Giovanni in Laterano, Gesù, Sant'Ignazio di Loyola, Santa Maria del Popolo, Santa Maria in Trastevere and Santa Maria Sopra Minerva are on this list. LOL, my rule of thumb is that if I find a Roman church open, I take a peek! They're almost always free, and almost always interesting. You'll note that I left St Peter's Basilica (and Vatican Museums) off the list. Sure, do them if desired but be aware of overwhelming crowds. There is very recently the possibility of booking timed-entry tickets to the basilica for a fee to avoid waiting in the 'free' line. The Museums also involve timed-entry tickets for a fee and should always be booked in advance.

Baths Of Caracalla: an idea of just how enormous these complexes could be!

I'l throw a visit to one of the ancient catacombs onto this list. Specific mentions are San Sebastiano or San Callisto (both out on the Appia Antica, a very interesting part of Rome) and Priscilla.

To save time I'll just highlight what Kathy said and strongly agree.

I'll just mention that I'll personally advise booking a guided tour
that includes the Colosseum, Forum and Palatine. The Colosseum's own
website doesn't offer one of these so you'll need to use an
independent company (Through Eternity, Roman Guy, etc.). The Colosseum
is easy enough to understand on your own with an audio guide or
advance reading but the other two sites are important, much more
complex, and really benefit from a human guide to shepherd you through
and explain what you're looking at.

I liked the Colosseum, but loooved the Forum and Palatine Hill. We used Through Eternity Tours which brought what we were seeing to life.

Thanks so much Mae, Kathy and Allan, truly wonderful tips!

I will be sitting on my computer trying to get a couple of tickets for our dates….I have a few days up my sleeve.
It sounds like a wonderful experience.

We are staying in Trastevere, any recommendations on restaurants?

Thanks again. ☺️

Hi Mae
I just sent you a direct message. Thank you in advance

I would just add that San Clemente [near colosseum] is pretty amaxing if you buy the ticket to see the excavations, as you descend you travel back in time, the main church [no ticket required] is 12th century, the next level down [ticket required] is a 4th century church, the next level down is a 1st century Roman Temple [Mithraeum] with a school rome and street - there is nowhere else in Rome where you see the layers of the city one on top of the other, in this way.

My favourite restaurant is AL34, and Roscioli is pretty good as well - booking definately needed for Roscioli.

A slightly 'left field' suggestion would be freetour-dot-com 'Who Killed Caravaggio' walking tour - we went with several friends none of whom are very into art, and they went back to the churches on the tour the following day to look at the art again. It was great.