Tunnel 57 was a tunnel under the Berlin Wall that on 3 and 4 October 1964 was the location of a mass escape by 57 East Berlin citizens to West Berlin. It was built from the basement of an empty bakery at 97 Bernauer Straße in West Berlin, under the Berlin Wall – which at that time and place consisted of empty, bricked-up apartment buildings on the east side of Bernauer Straße – all the way to a disused outhouse in the rear courtyard at 55 Strelitzer Straße in East Berlin. At a depth of 12 meters (39 ft) and a length of 145 meters (476 ft), Tunnel 57 was the longest, deepest and most expensive flight tunnel built in Berlin. Thirty-five West Berliners, including Wolfgang Fuchs, the future astronaut Reinhard Furrer, and many students from the Freie University in West Berlin, helped to build the tunnel from April to October 1964, until on 3 and 4 October 57 people fled the GDR via the tunnel.