The relationship between natural environment immersion and psychological wellbeing represents one of the most compelling yet underexplored dimensions of urban wellness tourism. This study investigates the influence of immersion in natural environments on the perceived psychological wellbeing of foreign tourists participating in mindfulness-based wellness programmes in Colombo, Sri Lanka, an urban-coastal metropolitan destination experiencing rapid wellness tourism growth. Drawing on Attention Restoration Theory and Stress Recovery Theory, a quantitative cross-sectional design was employed, with data collected through structured Likert-scale questionnaires administered to 374 international wellness tourists at luxury hotels, yoga studios, and specialised wellness centres. Descriptive statistics revealed uniformly high agreement across all five facets of natural immersion (mean values: 1.77–1.83). Chi-square analysis confirmed a statistically significant relationship between natural environment immersion and psychological wellbeing (χ² = 340.217, p < 0.001). The findings affirm that access to coastal and green natural settings is a primary psychological restoration mechanism in urban wellness tourism contexts. Practical implications are offered for Colombo’s wellness destination stakeholders, with broader applicability to urban-coastal tourism destinations in developing Asia-Pacific economies.