In the 1930s Potsdamer platz was one of the liveliest places in the city with hotels, restaurants and shops. However, with the division of Berlin, the square was heavily destroyed by bombing, it's at the junction of the British, American and Soviet sectors. It's a desert town, a no man's land between the two walls. In Potsdamer Square you can find several fragments of the wall and a control tower which is about Erna Berger Strasse. You can see the wall "below", that is the part that was buried in the ground to reinforce the structure, and as the pieces are cut loose you can see the inner structure.