First, look upwards to take in the splendor of the world’s largest unsupported dome. Later you can climb to the top of the dome for a fantastic panorama view of Rome. Upon exiting the basilica, turn left and loop around to the right of the portico. There are over 550 steps, and it costs 8 euro to go up, or 10 if you take the elevator. Do not attempt it if you feel claustrophobic.