In recent years, adventure sport tourism has emerged as a transformative form of travel that combines physical challenges with emotional and psychological growth, particularly in eco-adventure destinations. Despite its increasing popularity, empirical research on the psychological outcomes of such experiences remains limited. This study aims to investigate the impact of structured adventure sport tourism packages on the psychological wellbeing of tourists in Indonesian eco-adventure destinations. A quasi-experimental design was employed with 60 participants aged 18–45, divided into an experimental group (n = 30) and a control group (n = 30). Psychological wellbeing was measured using Ryff's Psychological Wellbeing Scale (RPWB) and the Positive and Negative Affect Schedule (PANAS), administered before and after a 3-day, 2-night intervention. Additionally, semi-structured interviews were conducted with selected participants to capture qualitative insights. The results revealed a significant increase in psychological well-being in the experimental group compared to the control group (Δ = 12.73, p < 0.001, Cohen's d = 1.78), with notable improvements in self-acceptance, environmental mastery, and purpose in life. Qualitative data supported these findings, indicating enhanced emotional restoration, self-confidence, and social connection. The study concludes that eco-adventure tourism has strong therapeutic potential as a non-clinical intervention to improve mental health. These findings offer theoretical contributions to positive psychology and practical implications for sustainable tourism development strategies.