While autumn hues color the Mid-Atlantic, the landscape in our favorite nearby cities — Washington, Philadelphia and New York — is equally luminous with vibrant arts, entertainment and cultural activities. Four phenomenal fall festivals in Philadelphia premiere indoor, outdoor and pop-up performances of world-class opera, theater and groundbreaking art exhibitions. In New York, the Muppets score their own permanent gallery space and fashion is defined at the Museum of Modern Art. And down the road in D.C. are major museum openings and the pre-Broadway premiere of “Mean Girls” the musical. The days may have cooled down, but these cities are hot with many things to do. So check out our picks for the best places and events in each.