It's easy to get to the Vatican by taxi, bus or by foot from Rome—the closest neighborhood on the other side of the Tiber being Navona. A beautiful experience can be get to San Peter walking from Piazza Venezia, along Via del Plebiscito, Corso Vittorio Emanuele and then Via della Conciliazione or, if you want, from Termini, walking along Via Nazionale, in the closest aproximation to the Washingtonian "National Mall" or Parisian Voie Imperiale that Rome has to offer you. Take the Metro line A to Cipro for the Museums, or Ottaviano for St. Peter's, or the tram to Piazza del Risorgimento.
From Central Rome, the #64 bus goes right to the southern end of the Vatican, but it is filled with pickpockets so guard your valuables!
