The Empty Air is an interactive soundwalk of Philadelphias Rittenhouse Square Park, created by The Mural and the Mint. Go to Rittenhouse Square, launch the app, put on your headphones, put your phone away and go for a stroll. Each part of the park has its own distinctive audio experience. You must be in Rittenhouse Square to experience this app. Continued use of GPS running in the background can dramatically decrease battery life.