The Pennsylvania Academy of Art has a wonderful museum, but even better is their permanent art collection in the historic Landmark Building. It's filled with astonishing works, no suprise given that their alumni include Thomas Eakins, Mary Cassatt, Cecilia Beaux, Maxfield Parrish, Robert Henri, Charles Sheeler, John Sloan, and Arthur B. Carles!
This is a city that loves food. There are many small (10 tables or less) neighborhood restaurants to enjoy. My favorite was Tria, a wine bar at the corner of 12th and Spruce.
The mecca for foodies one-and-all is the Reading Terminal Market. Filled with fish mongers, produce stands, tiny lunch counters, bakeries, chocolatiers, Amish preserves... no one walks away hungry.
Just 30 minutes from Philadelphia is another cluster of amazing places to visit. There are important Revolutionary War battle grounds here and the Brandywine Museum, featuring the works of early American illustrators and a jaw dropping collection of Wyeth paintings; N.C., Andrew and Jamie. The Dupont estate, Longwood Gardens and Winterthur, are nearby. The heady flora scents and colorful displays in the Longwood greenhouses were a welcomed sight on a cold and gray wintery day. This would be an astonishing place to visit in warm weather when the fountains are running, the topiary garden is open, and the grounds are at their peak.