10 Hour lay over in Rome

Couple options Take the Leonard Express to Termini (30 mins), walk across the plaza in front of the station and one of the hop on/off bus that start there. Ride it around once to get a quick overview, and then decide which sites you want to visit as time permits on the second time around. You will not have time for big sites like the colosseum or the Vatican but you would time to walk by the Trevi fountain, Spanish steps, and Pantheon. Another would be to take the local train from the airport that stops at St. Peters and Trastevere, and with a good map walk across Rome to Termini and back to the airport. EDIT: PS Should have added that it would be about four to five miles from Vatican to Termini. To give you a sense of the time it would take to walk. Without stopping it would be about an hours walk on a direct line. Three to four hours would be a reasonable time period to walk and see some things.

I agree with Frank - you're either going to have time to tour 1-2 major sites or make a limited walk through the city. I'd go with the walk. The hop on/off bus would be a good option, but I like Frank's idea of taking the local train from the airport and get off near the Vatican. From there, with a good map you could walk back toward Termini and hit a bunch of sites along the way. Assuming you're in decent shape, I think you could see the Spanish Steps, Trevi Fountain, Pantheon, St. Peter's, and the Colosseum in that amount of time. You won't have a lot of time to appreciate everything, but you'll at least see some of the most famous sites.