As the embodiment of a border-crosser between science, literature, and occultism, the writer Stanisław Przybyszewski also represents the ambivalent consciousness of the avant-garde. Behind the facade of imperial Berlin, he opens up a world of wonder, demons and ecstasy. Without using a normative understanding of modernity, this article attempts to portray Przybyszewski as proof of the irreconcilable tensions between rationalism and irrationalism in the period around 1900. Central to this argumentation are his spiritual references, such as satanism and occultism.