Coastal public spaces in large Euro-Mediterranean cities represent critical zones of negotiation between land and sea, where ecological fragilities, infrastructural pressures and social demands intersect. Grounded in the concept of the urban amphibious condition, this study explores the spatial and functional complexity of city–sea interfaces through the development of CITI4SEA, a multidimensional framework designed to assess coastal public spaces across diverse urban contexts. By applying it to seven major coastal cities, the research constructs a comparative lens capable of highlighting patterns that transcend national boundaries. The analysis reveals the emergence of cross-national clusters, formed not by geographical proximity but by shared planning logics, morphological features and degrees of ecological and social integration. This comparative perspective allows to understand how different cities respond to similar coastal challenges, offering insights into the structural asymmetries that affect accessibility, environmental quality and public use. Beyond mapping differences, the study contributes an operational methodology for evaluating littoral transformations within the broader framework of Integrated Coastal Zone Management and Maritime Spatial Planning. In doing so, it proposes a replicable tool that can inform strategies rooted in local realities—where adaptability, equity, and spatial specificity guide the evolving relationship between cities and the sea.