The Mauerpark is a public park in the Prenzlauer Berg district. Mauer means wall, which is referring to its status as a former part of the Berlin Wall and the so called Death Strip.
800 meters of that Wall is still standing in the park today and part of it is a popular place for graffiti artists to paint and display their work (it's legal there - not that a f**k is given about the fact that it's not legal in most parts of Berlin). On the contrary to what is normal at the East Side Gallery (here) these works however are not meant to be kept and get painted over by the artists almost daily.
It was early and not very warm when we got there, but a few people were at work anyway.
In the one but last photo you see how thick the paint layers get. Thick enough to break of a piece and take it home, where it sits in my living :-)