The aim of my thesis is to critically explore how young people’s long-term wellbeing is influenced by participating at a nature-based intervention. Nature-based interventions aim to improve participants’ wellbeing by incorporating nature through regular, structured, and facilitated activities. There are growing concerns for young people’s mental health and connection with nature. The prescribing of nature-based interventions is a growing area for providing support for people’s mental health. There is a developing evidence-base regarding the efficacy of nature-based interventions in supporting short-term benefits to wellbeing. However, firstly, there are limited follow-up studies, so there is uncertainty regarding the longevity of benefits to participants’ wellbeing. Secondly, less attention has been paid to how these benefits occur with the roles of the facilitators and participants being particularly neglected. To consider these aspects I developed a theoretical framework which engaged therapeutic landscapes with person-centred psychotherapy to explore the role of relational dynamics in people-place encounters. I engaged with a range of in-depth qualitative and creative research methods to explore with participants and facilitators their situated lived experiences of nature-based interventions. Firstly, I recognise the generative capabilities of facilitators and participants and the role of their motivations, intentions, and nature connection in co-creating affective therapeutic places. Secondly, I highlight specific relational qualities of facilitators and the agency of participants in engaging with these to co-create therapeutic encounters that offer respite and transformation. Thirdly, I highlight the long-term influences on young people’s movement towards a fulfilling life through their developing sense of self, wellbeing practices, and life choices. Finally, I enhanced our theoretical understanding of the relational self in therapeutic landscapes. Specifically, I highlight why and how intra- and interpersonal relational dynamics are involved in enabling place-based encounters, which can have a long-term influence on young people after and outside the original therapeutic event.