People identify with their hobbies often which stimulate physical activity and participation in social activities, which in turn relate to higher levels of subjective well-being. Hobbies are potentially a powerful tool for design; however, it is unclear how to take hobbies into the design process for example to increase engagement. By creating and using the Leisure Time Canvas we identified older adults’ previous, current and potential future hobbies, and by closely collaborating with users we process these results into the design of a walking application called Ommetje. Thus, we demonstrate a design case to motivate physical activity. We present the design rationale of Ommetje and how we evaluated this smartphone walking application with 16 older adults for four months, and reflect on the design process of using hobbies as an ingredient for design. We show the power of hobbies in a design (process) as an intrinsic motivation to trigger people to be more socially and physically active.