Natural protected areas can provide sustainable recreational opportunities, but they are always facing negative impacts caused by visitors. Degradation of environment due to recreational use has attracted scientists and protected-area managers. As a result, a variety of assessment and monitoring methods have been developed by now. Conventional approaches include field-based surveys and repeat measurement of site-specific impacts, which has been widely used to monitor degradation, because of its easy implementation. Recent advances in technology enable the development of new methodological approaches, allowing for understanding not only point-specific, two-dimensional changes, but also to study volumetric transformations or collect time-series of spatially dependent data. These approaches include 3D reconstruction of the trail surface based on (1) unmanned aerial vehicle (UAV) photography and or ground-based photographs, which can be subsequently processed through the structure-from-motion (SfM) process to generate detailed digital elevation models, (2) terrestrial laser scanning (TLS); (3) GPS loggers; (4) time-laps cameras, etc. The development of the methodology would lead to better management of recreation in natural protected areas. This session will present the state-of-the-art methodologies of monitoring and assessment of environmental impacts of outdoor recreation in different environments, and discuss their application, which would be beneficial to managers of natural protected areas of high conservation value. We invite contributions from wide range of topics covering all aspects of outdoor recreation impacts and their sociological and environmental consequences. Studies linking direct field-based observations with modelling and predictions are particularly encouraged.