The <em>Art Nouveau</em> <em>Path</em>: Valuing Urban Heritage Through Mobile Augmented Reality and Sustainability Education

Cultural heritage is increasingly framed as a living resource for citizenship and education, although evidence on how in situ AR can cultivate sustainability competences remains limited. This study examines the Art Nouveau Path, a location-based MARG set across eight georeferenced Points of Interest in Aveiro, Portugal, aligned with the GreenComp framework. Using a DBR case study, it was analyzed repeated cross-sectional student questionnaires (S1-PRE N = 221; S2-POST N = 439; S3-FU N = 434), anonymized gameplay logs from 118 collaborative groups (4,248 group–item responses), and 24 teacher field observations (T2-OBS), integrating quantitative summaries with reflexive thematic analysis. References to heritage preservation within students’ sustainability conceptions rose from 28.96% at baseline to 61.05% immediately post-game, remaining above baseline at follow-up (47.93%). AR-supported items were more accurate than non-AR items (81% vs. 73%) and were associated with longer on-site exploration (+10.17 minutes). Triangulation indicates that AR and multimodality amplified attention to architectural details while prompting authenticity debates. Built heritage, mobilized through lightweight AR within a digital teaching and learning ecosystem, can serve as an effective context for Education for Sustainable Development, strengthening preservation literacy and civic responsibility, while generating interoperable cultural traces suitable for future reuse.