being the smallest state in the world of which just a measly 0.44 square kilometers (0.17 square miles) in land area and about half is off limits to visitors, hence walking is the only option in touring the Vatican City of which you can start tour walking tour at the Saint Peter's Square into the Saint Pater's Basilica (and the catacombs if you want) then to the Sistine Chapel and then parts of the Vatican Garden open to the public and finally to the Vatican Museums (or vice versa) and you can do all of these in just four hours or less. Walking is not hard to do here unless you want to go to the top of Sain Peter's Basilica to see the View (and pay extra too).
Walking is an ideal way to exercise your legs, body and mind especially on your vacation in a foreign country! Vatican City has a total area of just around 110 acres which is the smallest country in the world in terms of size and population. Thus all corners of the Vatican City are within walking distance.
Of course you may choose to stop and relax while walking wherever and whenever you like along the way in the city streets, to chill out in the bars or restaurants, to hunt for souvenirs at the many souvenir shops along the streets, to do some window shopping at elegant shopping malls or simply to visit the various tourist attractions in the city!
It's easy to walk to the Vatican from Rome (and/or take public transportation), and within the Vatican, you can walk. It's small enough not to need a car or other mode of transportation, and it's the best way to enjoy your visit there. Be sure to wear comfortable shoes! I may be wearing strappy high heels in the pic, but consider that I'm a dancer (we have tough feet) and that when I left the hostel that evening I didn't expect to end up traipsing all the way from the Spanish Steps to St. Peter's Square...
Walking from Rome to Vatican city is the best way to visit the Vatican city and its museum, as the bus could go faster than you can give a long sight and the studing of every place and monument, so best transportation are your feet ;-)