Human contact with the natural environment effectively counteracts negative symptoms of stress and has many positive psychological effects. For this reason, forests within city limits are increasingly seen as part of public health promotion. Being in an urban forest can take many forms, but there is still little known about whether being in a forest alone, without engaging one’s senses, is as effective for human renewal as an experience that involves greater, more conscious activation of the senses of sight, hearing, smell. A study measuring the effect of the forest (spring aspect) on human mental relaxation during passive exposure was conducted on a sample of 19 Polish young adults. The experiment consisted of two series. In the first, participants read an academic textbook in a tree stand for 20 min, while in the next session—conducted at the same location—they contemplated the landscape. Before the experiment and after each of the two series of tests, four psychological questionnaires were administered: the Profile of Mood State (POMS), Positive and Negative Affect Schedule (PANAS), the Restorative Outcome Scale (ROS) and the Subjective Vitality Scale (SVS). Analyses showed that being in a forest environment positively influenced the subjects’ mental relaxation, while the level of benefit from the activation of the senses, especially vision (looking at the forest) was significantly higher compared to the passive activity of reading a text. The research indicates that forest bathing is the best form of relaxation that can be obtained through contact with the forest.