The next Sunday (27 September, 2015) the city will host the Berlin Marathon.
This is one of most important sport events in Berlin, 42 km around the city passing through the most important points: Reichstag (6,5 km), Friedrichstadtpalast (8 km), Olivaer Platz ( 33,5 km), Potsdamer Platz (38,5 km), Unter den Linden (41 km) and the finish, obviously at Brandenburger Tor (42 km).
This year, between about 40.000 runners there are three of the best marathon runners in the world: Eliud Kipchoge, Emmanuel Mutai e Geoffrey Mutai, all of them from Kenya.
Other info here.
Picture from Bmw Berlin Marathon website.