Of all the great cities where a guided walk is a good idea to help peel back the layers of history, Paris leads the pack. Explore the Latin Quarter from a literary angle with the "Hemingway's Paris" itinerary, or the city as it was in the late 1700s with "The French Revolution." Focus on medieval and Gothic architecture and sculpture with "Ile de la Cité and Notre Dame." On "The Village of Montmartre" tour, wind around cobbled streets where such artists as Van Gogh and Renoir had their studios, and get a sweeping view down over the city from the steps of Sacré Coeur.