This paper investigates how official Instagram accounts of six major Spanish cities influence user engagement and contribute to destination branding. Drawing on a one-year dataset of posts, the analysis examines three forms of user interaction to provide a nuanced understanding of engagement dynamics. Findings confirm that Instagram is a central tool for tourism promotion, allowing destinations to showcase assets while conveying a distinctive "personality" that fosters emotional and cognitive connections with users. Engagement varies across content types. While images of iconic landmarks often attract immediate visual attention, cultural activities, gastronomy, events, and nightlife frequently elicit deeper responses, enhancing the city's multifaceted digital identity. Posts that encourage interaction generate more meaningful dialogue, highlighting the importance of diversified strategies tailored to marketing objectives and specific audience segments. User-generated content also plays a strategic role, strengthening emotional bonds and enabling co-creation between visitors and destinations. Cities that effectively manage their digital identity achieve higher engagement, positioning themselves more competitively in the tourism landscape. Ultimately, Instagram's effectiveness depends not solely on visual appeal but on the capacity to craft coherent, authentic narratives aligned with the city's personality. By integrating these strategies, destinations can attract and retain visitors more effectively, transforming digital engagement into sustainable tourism growth and long-term competitive advantage.