How is the term holiday defined today? Holiday is a gener- al term. For centuries it has referred to the period of time when a person stops working. Conversely, tourism is a special serum. Since the beginning of the 19th century it has been a holiday activity that fulfills a certain period of time in a special way. Contrary to what the modern typology of leisure admits, reducing tourism to a general concept and holidays to a special concept. (Urbain 2000, 19)

 Based on social tourism, sustainability and the substantial strengthening of the local community, we will try to investigate the way in which holidays are carried out in places of thermal interest of the past, today and a visionary tomorrow. Provisions for social tourism are today, for developed countries, an obligation of the state. A necessary condition for the development of social tourism is the existence of an active Social State and the creation/ maintenance of the appropriate infrastructure and reconstruction.

 The public tourist complex in Loutra of Kythnos, consisting of the Xenia hotel, the hydrotherapy center and two
thermal springs, is chosen as the object of research and design proposal.

 Loutra is a seaside traditional settlement of Kythnos in the Complex of Cyclades. It is located in the north-eastern part of the island and owes its name to the hot springs, which were known since the Roman period for their beneficial properties.

 The aim of the work is the proposal of a functional hydrotherapy complex, with bath and hotel facilities. Both the architectural and the programming axis revolve around the development of an economic and energy ecosystem that works for the benefit of the citizens, while at the same time it is an essential step in the development of local autonomy.