vatican

You could. You can also get your tickets/tour directly from the Vatican. We opted to tour the Vatican Gardens since the Vatican was the only way to do that, and we like our own speed in Museums. The tourguide was rather meh, but the gardens were great. I have heard some rumors around that you may now need a tour to take you from the Sistine Chapel to St Peter's through the back door. This use to be open to anyone in the Museum (and may still be, I haven't heard anything certain); either way, the garden tour wouldn't save you all the lines if this were the case (unless you booked another tour that covered St Peter's)

There are two doors when you exit the Sistine Chapel. One if four tours and the other is for those without a tour. The guards usually let anyone use the "guide" door but sometimes they don't. It's really hit or miss. If you can't use the "guide" door you just end up back at the front of the museums and then must walk around to the basilica. Donna

The plus side to not using the tour door in the Sistine Chapel is that you get to see the famous spiral staircase.

Get your tickets in advance (online) and you will skip the long long lines to get in. A tour guide would be a good thing, imho, in the Vatican Museums because there is just so much to look at. And with the crowds, with and without tour guides, pushing you along, it's easy to get overwhelmed.