Must be the entrance to a paint store.

That is the so called "Holsteiner Treppe" (Holstein stairs) in the german town Wuppertal. These stairs link Gathe Street (where the picture was taken) with Holstein street. The coloration was made during the art-project "Sieben Treppen) (seven stairs) by artist Horst Gläsker and his wife. On each stair you can read words loke friendship, love, mania, envy and so on. (http://de.wikipedia.org/wiki/Holsteiner_Treppe)