Midway Geyser Basin in Yellowstone National Park provides visitors with a unique opportunity to experience rare geothermal features, extreme environments and associated micro-organisms. These associated organisms are considered one of the world's most valuable resources for biotechnology innovations. In this study, the authors investigated the development of park visitors' knowledge, values and beliefs during their visit to the Midway Geyser Basin. The study draws on prior work in the areas of museum and informal education, public understanding of science and cognitive psychology. A total of 191 visitors were interviewed before and after their experience in the geyser basin. Results of the study include an in-depth description of the personal, social and physical contexts of the visitors' experience in the geyser basin. The results are interpreted in terms of park visitors' knowledge systems, how the experience stimulates personal understanding, knowledge construction and value development among groups of visitors. Conclusions provide a unique perspective on the role of typical park visitors' prior knowledge, on the social construction of knowledge during the park experience and on the development of complex value structures related to unique biological resources. Conceptually, the results indicate the value of using a theory of knowledge systems to help us to better understand learning in informal settings. Practical implications of the study include a number of cognitive 'anchors' or 'bridges' that can facilitate further learning by park visitors about these unique environments and associated biological resources.