When we think of travel between East and West Germany during the Cold War, we usually have the famous Checkpoint Charlie in mind. This crossing point between West and East Berlin at the Friedrichstrasse was only open to foreigners and members of the Allied Forces. Checkpoint Charlie was on of three Allied-controlled crossings. Of course, Checkpoint Alpha and Bravo existed as well: Checkpoint Alpha being the Helmstedt border crossing on the highway (Autobahn) connecting West and East Germany, and Checkpoint Bravo being the highway crossing between East Germany and West Berlin.
But another crossing point existed, although not for the general public: Glienicke Bridge. Or more commonly known as 'the Bridge of Spies'. This bridge crosses the Havel river, and connected the Wannsee district of Berlin, with the city of Potsdam. After WW2, the bridge was mainly used by Allied Forces traveling from the French, British and American Sectors of Berlin to the military presence in Potsdam.
In 1952 the bridge was closed to residents of West Germany and the Allied Sectors of Berlin. And after the construction of the Berlin Wall in 1961, it was closed for citizens of East Germany as well. Ironically, the government of East Germany choose to rename the bridge as Brücke der Einheit, Bridge of Unity, as is shown on the 1957 East German Map below.
On the 1962 JRO Sondernkarte Berlin, the bridge can be seen at the South-West Border of Berlin. On this map, the bridge is not named, but the open red dot indicates it as a checkpoint for control of Western Allied military missions and diplomats only.
Because the bridge was an easy to monitor crossing point between East and West, the United States and the Soviet Union used it as a place to exchange captured spies, or alleged spies. The first exchange that took place was that of the Soviet spy Rudolf Abel, and the captured American pilot Gary Powers, in 1962. But several more exchanges followed. The last exchange took place in 1986, much more visible to the public eye than ever before.