For those who never manage to create an iPhone playlist that delivers the right thing at the right time, Pulitzer Prize–winning composer Ellen Reid and the New York Philharmonic have created Soundwalk, a free app that plays music through your phone, programmed for each section of the park. A built-in GPS knows right where you are and how to give the setting an extra atmospheric layer, whether earthy or ethereal, which evolves with whatever way you turn. – WQXR