Rome - Italy
It's difficult to know where to begin in a city brimming with icons of antiquity and the Christian faith. Of course, your personal interests will influence your selections, but there are certain locations in Italy and throughout Europe that are virtually mandatory, such as the Colosseum and the Pantheon.
A word of caution: try to mix your encounters in Rome so that you don't visit too many historical ruins or cathedrals in a row. Intersperse these more important sights with a few that are merely tourist symbols, such as the Spanish Steps and the Trevi Fountain, where all tourists must go to fling their cent. Since Rome is so large, even the most ardent tourist should take some time to relax and enjoy la dolce vita at a park or sidewalk café.
While Rome's biggest tourist attractions aren't exactly clustered, most of them are within a 20 to 30-minute walk of one other, making various regions convenient for touring. The Monti area is the closest to the Forum, Colosseum, Trevi Fountain, and even the Spanish Steps and Borghese Gardens.