For some reason I just couldn't wait to get to Potsdamer Platz while we were in Berlin, I think I went on about it from the moment we landed. When we actually got there, there wasn't much of a square (as Platz means) at all, but plenty to see nonetheless!
Looking into an art installation by Pythonist Terry Gilliam
This un-square square must be the obvious spot to take your geometry class...
The Sony Center