If there is just one guided tour you do of Rome during your visit, we would highly recommend doing an evening walking tour of the city.
The centre of Rome (where the majority of the famous landmarks are) is fairly small and walkable, which makes a walking tour for this city perfect, as you can cover the main landmarks and get a good overview and history of the city within a 2 hour tour.
The reason we recommend an evening tour, especially in the summer months, is because of the heat during the day. Not only is the heat fairly intense, but the old cobbled streets are uneven and the two combined can make uncomfortable walking conditions. In the evening you’ll benefit from the cooler air.
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