If you ever find yourself in Rome, you might think it's a good idea to hit up all the ancient Roman stuff in one day, and then do the Vatican stuff the next - especially since the Vatican is closed on Sundays and the other museums tend to be closed on Mondays.
Guess what is actually a really bad idea? Seeing all the ancient Roman stuff in one day. While it is relatively close together with a few exceptions, it still involves a lot of walking - no big deal, I'm used to my feet hurting by the end of the day when I'm traveling. More importantly, however, a lot of that stuff is outdoors, or at least has large outdoor sections, such as the Colosseum, the Forum/Palatine area, Trajan's Market etc. In other words, I'm in serious pain right now. I didn't expect Rome to be as hot as it is, I didn't even think to pack sun screen, and I'm rather fair skinned and avoid the sun. I can't remember the last time I had a sunburn but I've definitely got one now. (In Iraq, I tended to be rather more fully clothed, and for some reason, even the parts of me that were revealed to the sun just got darker - granted, I usually burn on my back and chest area, not my forearms.)
Besides that, Rome is gorgeous and I haven't even needed to use a bus or a subway to get anywhere yet, though given the condition I'm in right now, I'm seriously considering calling a cab in the morning to get to the Vatican. Not really. I also can't decide if I should be sightseeing or shopping because they have so many stores. I had dinner at the Piazza Navona last night, and a midafternoon snack there this afternoon when my feet couldn't take it anymore - so pretty.