[in Dutch with English abstract: ] The Hortus botanicus Leiden starts off with the Hidden Biodiversity project in October. Over the following years, this project will concentrate on enigmatic groups of species in an urban context. In this article, we introduce to you Tim Claerhout. As a PhD candidate for the following four years, he will investigate the urban diversity of epiphytic bryophytes and lichens. This will happen under the supervision of the prefect of the Hortus, prof. dr. Paul Keßler, dr. Michael Stech, Naturalis and dr. Laurens Sparrius, FLORON. Join Tim in an adventure from the grandiose landscapes of his youth to the small, inconspicuous life forms, and back to the enormous importance of these towards conserving urban biodiversity.