This study investigated the motivational and emotional experience of an experienced outdoor activity participant during a three-day guided adventure trek in Colca Canyon, Peru. The research adopted a qualitative autoethnographic approach which provided unique data in the form of diary entries, experiential diagrams, field notes and email content. An established theoretical model (reversal theory) was used to analyse dynamic psychological states and emotions that occurred in relation to changing circumstances during the trek. Overall, the data indicated increased positive motivational experience over the course of the adventure trek. Achieving trekking goals, experiencing scenery, views and the natural environment, and social interaction with other trekkers, guides and local people were key aspects found to positively influence the subjective outdoor leisure experience. The present autoethnographic study provided an in-depth prospective account of the participant's increasingly pleasant positive experience as the trek advanced.