Every five years, hundreds of thousands of art fans converge on the industrial town of Kassel, Germany, for Documenta, a grand quinquennial art exhibition inaugurated by the German government in 1955 to restore advanced culture in the nation after World War II. This past summer some 860,000 people made the pilgrimage.

On Tuesday, some rarities from Documenta 5 and 6, which took place in 1972 and 1977, respectively, went on view at Soho’s Goethe-Institut in an exhibition organized by the artist Christian Philipp Müller, who lives in Kassel and spent months combing through Documenta’s voluminous archives. It’s a highly personal selection, according to the show’s curator, Jenny Jaskey, who oversees a bibliophilic exhibition series at the Institut called “The End(s) of the Library.” The fifth Documenta included artists who have influenced Mr. Müller, and the sixth was the first one he saw.

Titled “Elective Affinities” (after the Goethe novel), the show, conceived as an artwork in its own right, includes correspondence from artists and curators planning their Documenta contributions. For some, like Michael Asher and Harald Szeemann, who both recently passed away, the show serves as a modest tribute to their careers, which marked milestones in Kassel. It also includes a trove of archival images—more than 2,400 pictures of the 1972 exhibition come from Mr. Szeemann’s archive, which was recently acquired by the Getty—that are displayed in the form of a digital slide show.

There are some highly unusual items in the Documenta archives. “The biggest highlight will be these Joseph Beuys walking sticks, which to our knowledge have never been seen before,” Ms. Jaskey said, speaking of the shaman-like German artist. They were given to Documenta founder Arnold Bode as a birthday gift.