Traditional turn-by-turn navigation approaches often do not provide sufficiently detailed information to help people with a visual impairment (PVI) to successfully navigate through an urban environment. To provide PVI with clear and supportive navigation information we created Sidewalk, a new wayfinding message syntax for mobile applications. Sidewalk proposes a consistent structure for detailed wayfinding instructions, short instructions and alerts. We tested Sidewalk with six PVI in the urban center of Amsterdam, the Netherlands. Results show that our approach to wayfinding was positively valued by the participants.