Treblinka II was a German Nazi extermination camp that operated from July 1942 to November 1943. Around 800,000–900,000 Jews were murdered there, mostly from Poland but also from other European countries. On 2 August 1943 the prisoners staged a revolt in the camp. Today the site is commemorated by a monument surrounded by a symbolic cemetery of around 17,000 stones. The audio guide, in the form of a mobile app for Android and iOS phones, leads visitors around the site of the former camp and presents its history and the fate of its victims. It allows the memorial to be visited independently, at your own pace. The app is available in Polish, English, German and Hebrew.