Hydrothermal karst is a process of dissolution of cavities in the rocks under the action of hot waters. In most cases these waters ascend, and transport the heat from the deep-seated parts of the Earth’s crust and lack any genetic relationships to recharge from overlying or directly adjacent surfaces. Hydrothermal karst, thus, is a special case of hypogene karst. Formation of hydrothermal caves may involve a number of mechanisms, which correspond to different temperature, chemistry of waters, and hydrogeological settings (subaqueous or subaerial). Hydrothermal caves have characteristic morphology and may host secondary hydrothermal mineralization.