Background: Physical inactivity is a contributing factor in the development of noncommunicable diseases (NCDs) and is one of the leading risk factors for premature death. Stair climbing offers a low-threshold strategy to increase physical activity levels in everyday life. Empirical findings report positive effects of so-called “nudges” in connection with measures to promote physical activity. Aim: This paper presents the nudge-based pilot intervention “Marburg. Geht doch!” and examines its effect on low-threshold physical activity (stair use). Methods: Differences in stair use behavior were tested by nonparticipant observations before and 2 weeks after the nudge was delivered using a standardized observation form and feedback interviews with passers-by (n_BZP1 = 2118, n_BZP2 = 2149). Bivariate analyses using cross-tabulation and subsequent chi-square test (χ²) were performed. The univariate analysis of the structured feedback was based on frequencies. Results: A nonsignificant increase in stair use was observed as a result of the intervention. Stratified by gender, a significantly higher stair use of about 4% could be observed for women during the second observation (χ² (df = 1) = 5.361, p < 0.05). While no significant differences could be found for age, nonhomogenous differences in stair use were identified depending on the observation location. The feedback interviews indicated a positive evaluation of the nudging intervention for the majority of the respondents. Conclusion: Although a significant improvement in stair use could not be found for the population observed in this study, the results still provide evidence for the potential of nudging interventions to promote an active lifestyle. Future interventions should pay greater attention to content and design, be gender-specific, and use appropriate evaluation designs.