Starting at the zoo, I crossed the Rhine River by cable car. From there I walked south through what once was the BUGA 1957 exposition, crossed the Deutzer Bruecke, strolled through the Altstadt and walked north back to the Zoo. The pictures I took at the Cologne Sculpture Park can be found in the Art & Culture section.
In all, a nice 5h hike through my most favorite German city - Koelle alaaf you!