The article deals with the topic of the architecture of digital collections presented in the Polish Digital Equestrian Library (Polska Cyfrowa Biblioteka Jeździecka), which is an example of an innovative library-thematic portal. The analysis was based on the nine principles of a good digital collection according to the National Information Standards Organization (NISO). Moreover, the case of the horse stud in Janów Podlaski, as an exemplary search term in the PCBJ catalogue, was presented. The results of the search about the horses’ stud in Janów Podlaski constitute a smaller percentage of the entire collection, but their value is because these materials are unique and can deepen the knowledge about the most famous Polish cultural heritage in the world.