Manual wheelchair users experience numerous invisible barriers while navigating cities, often reporting how stressful journeys are. This stress affects a wheelchair user's quality of life. To alleviate such psychological burden, we propose a novel intervention strategy with a respiratory biofeedback interface which is designed to help users feel relaxed in urban navigation. We conducted a study in a real-world setting to explore its potential to provide real-time psychological support. From qualitative and quantitative analysis, we report on the strengths and weaknesses of the approach.