Mentioned by Lonely Planet Top Choices
Top things to do in Rome, Italy
"Up to a third of the Vatican is covered by the perfectly manicured Vatican Gardens, which contain fortifications, grottoes, monuments, fountains, and the state's tiny heliport and train station. Visits are by guided tour only – either on foot (two hours) or by open-air bus (45 minutes) – for which you’ll need to book at least a week in advance.After the tour you're free to visit the Vatican Museums on your own; admission is included in the ticket price."