Purpose: This study aims to explore interdisciplinary and transdisciplinary interactions around sustainability, focusing on the United Nations sustainable development goals (SDGs). By using the city as an informal learning space, it presents a case study to raise SDG awareness, promote interdisciplinarity, foster critical thinking and empower students. Design/methodology/approach: Using qualitative content analysis, this study explores students' interdisciplinary engagements. The research centers on student-created Logbooks, combining field data for analysis via open coding. Findings: The informal setting facilitates transdisciplinary interaction and enriches interdisciplinary skills while retaining individuals' disciplinary tendencies. Research limitations/implications: Factors like local geographical conditions and participant numbers could lead to minor variations in future course applications. Although initial problem topics and discussions are confined to local urban geography, they might diversify during implementation. Practical implications: The Logbook serves as a guide for local urban issues and embodies interdisciplinary outcomes. It can be enhanced with maps and problem zoning. Social implications: Demonstrates effective SDG integration into higher education. Originality/value: This study spotlights interdisciplinary learning within an unconventional context -- urbanism -- bridging student gaps. Supported by a paradigm shift from sustainability to unsustainability, it underscores the significance of critical engagement with SDGs.