Help me fit the smaller stuff in!

Not to start off pedantically, but when you say “St. Mark’s,” I presume you mean St. Peter’s, as St. Mark’s is in Venice. As for other stuff, which, being in Rome, none of it is small: :-)

Baths of Caracalla could easily take several hours if you like to study the mosaics and wander and get a sense of how immense the whole complex once was, but it’s on the way to the Appian Way (and sort-of in the general direction of Ostia Antica, too), so would make a good combination. Ostia could take a couple of hours, or also all day. While coming back from the Appian Way, we toured the catacombs of Saint Sebastian, which include emerging into a church with Bernini’s very last sculpture.

You’ll see other remarkable Berninis. at the Borghese Gallery, of course. Book a reservation there right before (or during) lunchtime; the grounds and the gallery lobby seemed less chaotic. Wherever time you go, would this work on Day 4, after the Vatican?

Welcome ot the forum!

I hate to tell you but you don't really have time for much more at all.
It will be blazing hot in July. I'd actually try to. pick some indoor venues rather than outside

If you go to Ostia Antica- that will take the better part of a day. There is a bit of shade there but it's still July!

You could do Aventine and Baths of Caracalla on your Colosseum day as they are sort of in same vicinity. The Baths are huge and will take a lot of time.

Appian Way and Catacombs are well outside the walls of Rome and need the better part of a day. I believe you need a tour/guide . to see the catacombs. Maybe fit after Vatica.- but even with that 7:30 start you are probably not done at ST. PETER's til 12-1. It's an exhausting visit.

Capuchin Crypt are really cool/creepy- inside and don't take a huge amount of time, also close to Borghese- I'd definitely urge you to see the Galleria (you will need to prebook) it is one of the best museums in all of Europe. 2 hour limited timed entry so again not a huge time suck.

Be sure you allow time to just wander- enjoy the markets and piazzas, eat gelato.

We find that ONE large sight per day is our limit.
Colosseum/Forum OR Baths of Caracalla for example. Then spend the afternoon chilling, popping into smaller churches- they are on every corner- full of amazing art, free and nice and cool inside, sitting in a plaza people watching, resting at our hotel to get out of the heat!, then out again for evening apertivo and dinner.

Hahaha omg yes I meant St. Peter's. Too much travel reading today! We're visiting Venice later in the trip.

These are helpful responses, thank you. I think maybe we'll consider either the baths or Ostia Antica for that empty day and then include the Borghese Gallery around lunch/afternoon as you suggested. The weather here is about the same (yuck) so we are somewhat used to it. I figured we would head back to our hotel for a few hours each afternoon to cool off/rest. I haven't seen many suggestions about cooler indoor attractions - most things that I've read said the museums also tended to be warm. Is that accurate?

hilarym99, air conditioning (when there is any) moves a little air and makes it slightly less hot - not especially cooler, let alone colder. Plan on dressing for heat wherever you go, but just make sure everyone’s shoulders and knees are covered for meeting the modesty requirements at St. Peter’s and any other Catholic church you might visit. A lightweight shawl/scarf will be handy for such occasions. A longer skirt or breathable pants, too.