If you're up for a bit of a climb, I cannot recommend enough doing the Dome Climb at St. Peter’s Basilica! The views of the city are amazing, and it's incredible to get close to the gigantic dome and the huge statues that dominate the rooftop and look down over St. Peter's Square.
CLIMB OPTIONS:
Elevator + 320 stairs
Stairs only 551 stairs
I recommend using the elevator (PLUS stairs) option. The final few flights of stairs are in a tight space, so it might be a bit of a challenge if you're claustrophobic.
Try to visit first thing in the morning before the line ups get too lone.
You MUST buy your tickets at the Vatican Dome Climb ticket booth, not online. A sign pointing to the ticket kiosk is near the basilica's entrance.
After the climb, you'll end up in the basilica. If you do the climb early, you'll end up inside St. Peter's when it's not as crowded. Enjoy and spend a little time here.
HOURS: April to September: 7:30 am to 6:00 pm and October to March: 7:30 am to 5:00 pm. Closed Wednesday mornings for the papal audience.