Weīve been in Romre last May for a weekend and used the hopon-hopoff buses. Costs for 2 days was 22 euro p.p.
It was a nice way to get around rome without having to use the public tranport, which, on some routes is famous for its pickpockets... You can do much walking if you want to, if you donīt wannt or canīt, these buses are quite well.
Everyone receives headphones (new ones

) and the tour is audible in I believe 6 languages...
If you are visiting rome on a sunday, be aware that collosseum as well as basilika st.pete are not stopped at... on all other days, these are regular stops.
If you have any further question, donīt hesitate to ask.
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November 2005 - Costa Marina (Spanien und Kanaren)
Mai 2007 - Costa Victoria (öst. Mittelmeer)
Oktober 2007 - NCL Gem
November 2007 - Costa Fortuna (Karibik)