This publication is devoted to a little-known temporary artwork of Thek’s, made in the winter of 1973/74 while he was a guest of the Lehmbruck Museum in Duisburg. His expansive environment Ark, Pyramid–Christmas (“The Manger”) filled a whole room. This exhibition, organised by the director of the museum at the time, Siegfried Salzmann, was the fourth in Thek’s series of atmospheric, large-scale projects in Europe, which engaged with individualised religious symbols. The festive period provided Thek with the occasion to present, for the first time, a self-written theatre piece in the form of a nativity play featuring children from Duisburg. A great quantity of original material and documents have been discovered in the museum’s repository and enable a reconstruction of the exhibition in this book, accompanied by an interview that Marietta Franke conducted with Franz Deckwitz, who helped with the installation in 1973.