The subject of research in this paper is the European cultural route of historical thermal cities. The goal of the work is to explore the rich cultural and historical heritage of European and Croatian spas, and the purpose of the work is to reflect on the development potential of our spas based on the analysis of European models of good practice and the advantages of international networking through the European Route of Historic Thermal Cities. The priority of cultural routes is and will remain culture. Research, education, heritage, creativity and tourism are welcome, but the basic elements remain meeting others and cultural exchange. Programs must convey the basic values of the Council of Europe: human rights, democracy, rights, tolerance, solidarity. The cross-border and European dimension can contribute to the interdisciplinary aspects of the project, developing awareness of multicultural identities. European spa towns were places of development of cosmopolitan culture, where members of all social classes could socialize, exchange ideas and create the leading scientific and artistic achievements of their time. The development of prestigious hotels and a rich offer of recreational activities, from the first casinos and theaters to covered promenades and landscaped gardens intended for the entertainment of classy tourists, guaranteed the lasting success of European spa towns. Even today, their visitors can enjoy festivals, events and numerous artistic and creative activities. Like other programs of cultural routes, the Route of Historical Thermal Cities, by traveling through space and time, shows how the historical heritage of different European countries represents a common cultural heritage. Participation in such a cultural route certainly presupposes consideration of the sustainable development of the destination. Also, being a member of one such route represents an opportunity for the development of Croatian spa destinations and a contribution to the promotion of European and Croatian spa heritage. A sustainable development path will strengthen Croatia's profile as an attractive destination, acting as a factor of local, regional and national economic well-being, while also contributing to transnational intercultural dialogue.