Separation from nature may contribute to stress and reduced well-being. Shinrin-yoku may be an effective and cost-effective method to improve mental health by immersion in forests/woodlands. This study experimentally tested the effect of Shinrin-yoku on stress, affect, and well-being and sought to gain further insight into the experience of participating in Shinrin-yoku. A mixed methods experimental design was used to conduct the study. A total of 22 participants, stratified by hand, were assigned to one of two conditions: the actual nature (Shinrin-yoku) condition and the digital nature (digital Shinrin-yoku) condition. Scales were used to measure four aspects of mental health: stress, positive affect, negative affect, and well-being. Participants completed 4 h-long sessions and questionnaires were completed at four time points: baseline, 2-week point, postintervention, and 1-month follow-up. A mixed between-within analysis of covariance was used to analyze the questionnaire data. In addition, participants took part in interviews and gave answers to open-ended questions, which were analyzed using thematic analysis. Actual Shinrin-yoku was found to increase positive affect and well-being significantly more than the digital Shinrin-yoku condition. This significant difference for positive affect between the two conditions remained at the 1-month follow-up. A number of themes were identified characterizing similarities and differences between the Shinrin-yoku and digital Shirin-yoku conditions. Positive emotions were experienced in both conditions, but although Shinrin-yoku was associated with mental refreshment, the digital Shinrin-yoku condition was associated with loss of concentration.