Checkpoint Charlie is the most known German-German border crossing and was a point to enter East Berlin. You can find a replica of the old guard-house, where officers were controlling border crossers, in the middle of Friedrichsstrasse.
Checkpoint Charlie only let through diplomats, foreigners and relatives of the allies. The museums house of Checkpoint Charlie, representing the history of the wall, opened in 1963. Keep in mind that the museum has an entrance fee.
Checkpoint Charlie became a symbol of the Cold War, representing Germany’s separation.