I bought a (more or less) mysterious box:

All I knew about the background was that it could be a psychological test, at least it probably comes from a practice or institute…

An enquiry to Prof. Helmut Lück from the Psychologiegeschichtliches Forschungsarchiv (Research archive on the history of psychology) of the Fernuni Hagen resulted in a reference to Prof. Kurt Gottschaldt. And this hint then led into the right direction (Geman): It is a Würfelkasten (cube box).

Kurt Gottschaldt became professor and director of the Institute of Psychology in Göttingen in 1962, which is probably how the box end up at the household liquidator.