Many of Rome's top attractions are within walking distance of each other, so comfortable shoes are a must. To get to Vatican City, take the Metro A line to Ottaviano-S. Pietro station. A taxi from the city center to the Vatican will cost around €10-€15, and buses and trams are also available.
If you have more time, consider visiting the Pantheon and the Trevi Fountain. For art lovers, the Borghese Gallery is a must-see, but be sure to book tickets in advance. If you have less time, prioritize the Colosseum and the Vatican museums, as these are the city's most iconic attractions. Don't forget to bring water and snacks, as it can get hot and crowded in the summer months.