The high prevalence of mental health problems among the growing population of older adults is alarming. Promoting park use is one strategy to improve older adults’ momentary emotional wellbeing and long-term mental health outcomes. However, to optimally promote park use among older adults, insights into park use aspects (i.e., nature contact, physical activity) and park elements (i.e., biodiversity and presence of loitering teens), and their interactions, that affect emotional well-being are required. This project aims to examine whether and how the causal effect of nature contact during urban park use on emotional well-being can be modified by engagement in walking and by biodiversity and presence of loitering teens. These effects are first examined during virtual reality (VR) experiments which enable to examine the effects under controlled conditions. Next, a within-person encouragement design is developed and applied, to examine the effects under real-life circumstances.