It is important that the ontology captures the essential conceptual structure of the target world as generally as possible. However, such ontologies are sometimes regarded as weak and shallow by domain experts because they often want to understand the target world from the domain-specific viewpoints in which they are interested. Therefore, it is highly desirable to have not only knowledge structuring from the general perspective but also from the domain-specific and multi-perspective so that concepts are structured for appropriate understanding from the multiple experts. On the basis of this observation, the authors propose a novel approach, called divergent exploration of an ontology, to bridge the gap between ontologies and domain experts. Based on the approach, we developed an ontology exploration tool which allows experts to explore an ontology and visualizes the result in a user-friendly form, i.e. a conceptual map, depending on the viewpoints that they specify. We evaluated the system through its application to an environmental domain and an experimental use by domain experts. As a result, we confirmed that the tool supports experts to obtain meaningful knowledge for them through the divergent exploration and it contributes to integrated understanding of the ontology and its target domain