St. Peter's dome has a height of meters from floor 136.57 Basilica to the apex of the crowning cross, making it the highest in the world. With its roof open best in Rome. But even if you have a paid lift to the top floor of the dome would have to climb back up, that should be considered for people suffering from claustrophobia and people.
To get to the dome of St. Peter's Cathedral in Rome, you must leave the Cathedral and go for pointers "Cupola" (if facing the Cathedral, then you must go to the right). Specify the time of the opening of the Cathedral and the dome on the desired date in the specified site