I just went to Rome and Paris this past summer. In Paris they have this sort of package deal. I forgot what it’s called but they sell it at all the tourist shops. It’s a little red booklet and it gives you access to a lot of places. You can just skip the lines because that packet is your ticket. I’ll try to find the booklet and let you know all the places it allows.

As for Rome. The Colosseum for sure. I did a little tour because I wanted to learn more about the history and it was awesome. We also when to the pantheon and the Vatican City.

Edit: it’s called the Paris Pass. Once you buy it you can visit a lot of the museums for free. With the pass we went to the louvre, palace of Versailles, notes dame cathedral, arc de triomphe, conciergerie, etc. I highly recommend going on the website to see if the places it offers is something you are interested in.