Grand Tours were seen as educational and social journeys which properly cultured the elites who participated in them. In its fully developed form the Grand Tour was often pretty formulaic. The route, destinations, and objects of interests (like palaces, statues, etc) were generally all laid out in advance and often prescribed in various guidebooks. It was also fairly common for a guide to accompany the traveler on the tour to help facilitate the educational and culturing process.
A lot of the focus on these tours was the classical culture of Old Europe, so places like Rome, Venice, Paris, etc were generally high on the list. Travelers would see the palaces and monasteries, statues and monuments, all the stuff that was meant to exemplify the greatness of European civilization. But don't confuse the Grand Tour with modern tourism. These aren't the Griswalds sidestepping their way through the Louvre. These were often ritzy private tours undertaken by the elites. They stayed with other noblemen, sometimes for months at a time in a single place, with fine dining and parties. It's a highly social celebration of the greatness of civilization, which helps explain why part of the decline of the Grand Tour is attributed to the rise of more Romanticized travel focused on nature and personal discovery.
hi! you'll find a few more morsels of info in these threads