The very popular location-aware travel guide app Detour usually cost $5, but for the rest of this summer it’s absolutely free. With 16 U.S. and international cities currently covered, including NYC, Boston, San Francisco, Rome, Berlin, Barcelona, and Paris, the audio walking tour app offers discrete hour-long guided tours narrated by local experts. Along with more than 150 separate walks, the app also features augmented reality that allows users to reveal historical location data. Check it out for yourself here, but don’t wait because the free offer ends on September 4, 2017.