Entry to the dome is to the far right of the basilica's main portico. A small lift takes you halfway up, but it’s still a long climb to the top (320 steps to be exact). Press on and you’re rewarded with some stunning views over Rome's rooftops. It’s well worth the effort, but bear in mind that it’s a long and tiring climb and not recommended for anyone who suffers from claustrophobia or vertigo.