Numerous studies demonstrate the benefits of the role of nature, activities, and social interaction at nature-based interventions in improving participants' wellbeing. These health-enabling encounters between people and places have typically been framed in geography via the concept of therapeutic landscapes. Empirical studies and theory have primarily focused on the characteristics of physical and social environments of therapeutic landscapes, while understanding why particular relational encounters are affective in co-creating therapeutic experiences has been given less attention. This paper focuses on understanding the nature of a person, and of interactions between people, as a fundamental part of understanding the way in which nature-based interventions co-create benefits to participants' wellbeing. To consider this we turn to person-centred psychotherapy, where we draw on Carl Rogers' conceptualisations of the person and the therapeutic relationship. Person-centred psychotherapy highlights the importance of a non-judgemental, empathic, and authentic therapeutic relationship in providing an environment for change and that a person is agentic in perceiving and engaging with affective relations in co-creating therapeutic encounters. These encounters have the potential to alleviate and/or transform aspects of a person's sense of self. These shifts in a person's self-concept are part of a process, which enables the flow of benefits from an intervention into participants' daily lives. Our approach is underpinned by using interviews with facilitators and participants of nature-based interventions. We propose that developing geographical understanding of the relational impacts on a person's sense of self and actions has implications beyond health geography.