For just 5 euros you can climb all the way to the top of the dome of St Peter's Basilica. It's over 500 steps (300 steps if you pay an extra 2 euros to get a lift part of the way), and there are three levels of the dome you can visit. There's an indoor section where you walk around the inside of the dome, and then you climb extra steps to get to the outdoor part right at the very top of the spire of the dome. The views are absolutely breathtaking, and well worth the 5 euros and 500+ steps.
