It is indeed Frankfurt am Main (the only real skyline in Germany, we call it "Mainhattan"). The building in the 2 first pictures is called "The Cube" and is the home of the German Stock Exchange in a Frankfurt suburb called Eschborn. I worked as a consultant there for a while and the building is architecturally interesting. It is actually 2 buildings with the space between them enclosed completely and glass crosswalks every other floor; it was designed so that a fire could completely consume one half and wouldn't destroy the other, allowing the business to continue. Walking from one side to the other on the 20th floor is not for those with vertigo, although the crosswalks are fully enclosed, they are mainly made of glass! I had colleagues who would take the elevator down to the ground floor, walk across to the other side and take the elevator up - just to go to another office on the same floor...

Here's an inside view: