Karen, there's one ticket for everything in the Vatican museums, but St. Peter's is free. It's hard to pick out anything particular in the museums, there's so much there. If you're really interested in Greek and Roman artifacts, etc. you should buy a guide book before you go in--all the inscriptions in the museum are in Italian. You have to go alllllllll the way through most of the Vatican Museum to get to the Sistene Chapel. When you get about 2/3 of the way through, there's kind of a fork in the road. You can skip the " Borghese??? " apartment and some additional artwork and go straight to the chapel if you want. When you get to that point, turn right instead of left, unless you want to go through the whole thing. When you're leaving the Sistene Chapel, go out to the right again (the tour group exit)--that's a short-cut to St. Peter's square. One other piece of advice. Go to the Sistene Chapel before you go to St. Peter's. St. Peter's is so magnificent, that if you go there first, the Sistene Chapel is kind of a disappointment (at least it was for me).