Klein spent several months in the Rhineland preparing exhibitions and creating new works on site. Clearly, many of his visual and conceptual innovations were linked to his experiences over the Rhine, amongst which his monumental project for the Foyer of the Gelsenkirchen Opera House – in collaboration with artists from France, Switzerland and Germany –, perceived by Klein as the creation of a “European situation”. Far from the saturated and impenetrable Parisian scene, the painter enjoyed unequalled success and recognition that reached their apogee in 1961 at the Museum Haus Lange in Krefeld, in what was the biggest solo exhibition of his lifetime. A genuine intermediary, he built an effective network of contacts and friendships between France and Germany, loyal, in that respect, with the old avant-garde dream of a cosmopolitanism that reaches across frontiers.