Geographical relational thinking is an important part of geographical thinking. This descriptive research was conducted to seek evidence on students' ability to establish geographical relationships which could help teachers to foster their geographical relational thinking. Sixty-nine small student groups from six secondary schools in the Netherlands were observed when solving a mystery. All relationships students established were analysed and the SOLO-taxonomy was used to analyse how coherent their solutions were. The results revealed that students had difficulties with complex, abstract and physical geographical relationships. A large proportion of the groups also had difficulties understanding the interdependence of the relationships. These findings underpin the usefulness of activities like mysteries which offer opportunities to practise, assess and teach geographical relational thinking in geography lessons.