Locate a good guide and take a hike. It was rather amusing to watch a couple with guide book in hand walking the cobblestone sidewalks without slipping head first over the irregular steps.
So much to see, observe the Inca foundations being used for the colonial buildings, note that the street patterns have not changed since the Incas ruled Cusco. Explore the cathedral with the cuy/guinea pig being served at the Last Supper.
So much to see.