If you visit St Peters Basilica, one option once inside is to climb Michelangelo’s dome (cupola.)
There are two parts to climbing St Peters dome: You can take the (231) stairs or the lift/elevator to the first level, and wind up on the inside of Michelangelo’s dome. If you climb the dome to the first level, you can go out onto the roof of Saint Peter’s basilica and see the apostles! The second part is optional. It means taking the next 320 stairs to the tippy top. Not only is there not an elevator, but you will find a narrow single-file staircase that slowly spirals up, with the roof sort of slanting in towards you as you go. And at the very end, as it gets narrower and narrower, you will have a corkscrew staircase, with a rope to hang onto!
Courtesy of https://www.romewise.com/