Berlin Wall needs little (or no) introduction. Also little is left of the Wall at its original site, as it was rapidly destroyed almost everywhere. However, you can recreate it in your imagination as it's original location is marked by a row of cobblestones placed in the streets of the central Berlin.
Temporal exhibition presenting history of Potsdamer Platz and Berlin Wall next to Potsdamer Platz with few original pieces of the Wall placed where they would have been if the Wall still had been standing:
A row of cobblestones that marks the former position of the Berlin Wall:
Famous Polish "protest" song of 1970/80's called "Mury" (The Walls) by Jacek Kaczmarski: