CS3 is a RESONATE specific prospective longitudinal study in Plovdiv, Bulgaria, monitoring 1,500 individuals over a 12-month period. CS3 will explore whether nature contact mitigates the effects of everyday stressors (e.g. traffic emissions, financial worries) on mental health, and which biopsychosocial mechanisms underlie this. It will also include a sub-sample to investigate a rich selection of biopsychosocial resilience metrics including immune function, oxidative stress (e.g. chromogranin), stress hormones (cortisol) and general allostatic load biomarkers (e.g. cholesterol).