The starting hypothesis of HYDROCAL project is that the extreme climate conditions (determining the water recharge dynamics, existence of ice caps, permafrost layer, etc.) and the presence of volcanic deposits related to subglacial eruptions, imply particular structural and dynamical characteristics to those hydrothermal systems hosted at high-latitude calderas. Hence, HYDROCAL project aims at characterizing the structure and dynamics of hydrothermal systems in polar and sub-polar active volcanic calderas, evaluating any particularities due to their location at higher-latitudes. As case studies, we propose Deception Island (Antarctica) (DI) and Torfajökull (Iceland) (TO) calderas in order to establish similarities and differences among both examples to provide, at the end, a full conceptual and evolutionary model of caldera-hosted hydrothermal systems in polar and sub-polar areas. Particularities of the selected case studies directly related to their specific location (i.e. island vs. inland), geodynamic contexts and magma compositions will be considered since the beginning. Obtained results will be compared to the most documented and well-known active caldera hosting an hydrothermal system and located in a temperate climate: Campi Flegrei (Italy) (CF).