Dutch artist Zeger Reyers (1966) realized the project Onder-tussen (In-between) at the occasion of the exhibition Voorwerk 5. In reaction to the state of the building where Witte de With is housed, Reyers made an installation with oyster mushrooms for the second-floor toilets.

Reyers’s installation was part of a series of in-situ projects for Witte de With’s stairwell that has included works by artists such as Philip Akkerman and Willem Oorebeek.

Yet Onder-tussen is by nature less permanent than the other installations. The mushroom's development has always been and remains unpredictable; even if the installation were to be removed, its traces would be left behind in Witte de With’s building for eternity.