Indie filmmakers and Hollywood stars have packed their snow boots and are heading to the mountains of Utah for the first time in three years, as the in-person Sundance festival returns Thursday. Co-founded by Robert Redford, and held in wintry sub-zero temperatures at an altitude of 7,000 feet (2,150 meters), Sundance's screenings and panels are a key launching pad for the coming year's top independent and documentary films.